So here's an attempt to do random cleric advancement that tries to account for the vagaries of worshiping a variety of weirdo gods. It's a step above the first random chart I made for clerics, and hopefully less time-consuming than writing a chart for each faith.. All first level clerics are the same as normal (hit dice, weapons, armor, saves, no spell, turn undead). For each spell slot you would normally gain via leveling up, roll on the chart below.
Basically, you define each god using 20 parameters:
[1st level cleric spell] - You know how 3e clerics can burn spells to power healing? This is like that only you can choose a different spell that's more appropriate. You can ignore the "1st level" or "cleric" designations if you want to, but don't over do it.
[location] - A place where your god has slightly more power/your cleric has slightly stronger faith.
[Lesser Miracle] - Some miscellaneous power, roughly equal to a 1st or 2nd level cleric or MU spell. If it's weak, designate it 3x a day (or at-will if it is really puny), otherwise list it as a daily power.
[Greater Miracle] - These can be as powerful as you want, but if they are really potent set them at once per session or just one use period.
[weapon] - The weapon used by clerics of this faith. If you have no idea, just select mace.
[enemy] - a group, race, or species loathed by the faith
[basic lore] - something many clerics of this faith know. Like many clerics of the god of blacksmiths know how to make stuff out of iron.
[secret lore] - a more advanced knowledge, or something actually secret, maybe even something campaign world important
[ritual activity] - something that clerics can do that would take maybe a single dungeon turn that would look pointless or dumb to non-believers but imbues the cleric with a little extra holy power
[object] - something material that is holy to the faith but not an actual holy symbol (like the chalice used at a Mass)
[ally] - a group that has good relations with the clerics of the god
[class] - a non-cleric class somehow relevant to the god. If you're using the DDG, check what class besides cleric the god has the most levels in. That's probably what you want.
[servitor] - whatever fulfills the role of angels for this god
[color or symbol] - a thing that a cleric could see that would fill them with renewed zeal
[clothing] - some sort of holy garb
[animal] - literally what sort of pet the god could send to a cleric
[element] - the force, energy, or element by which the god can smite enemies
[food] - something the cleric can hand out to allies, like communion wafers or witch's brew
[taboo] - something the cleric can do to cheese off the god
[time] - a part of the day, week, month, or year sacred to your god
Two things to keep in mind when setting this stuff up for your gods: It would be easy to overdo this stuff. Try to keep in mind the relative power level of your deity, especially when setting the two Miracles. Also, try not to be too consistent when developing this profile. Religions often look like nonsense to the outsider. A little inconsistency actually makes a faith more plausible.
I made a Google Form for this process, which dumps the results into a spreadsheet. I already put a handful of gods there to serve as examples of what I have in mind. Please consider using these docs so everyone can have access to a collection of ready-made cleric options. And if anyone knows how to do a mail merge in GDocs, let me know so we can output individual charts for each god.
(BTW, the Great Cosmic Flailsnail is a newly declared god. Zak almost stumbled across Its existence back in 2011, but he didn't realize that the titanic polyhedron he was describing was the shell of a multiversal snail-entity.)
Anyway, here's the chart:
Insano-Libs Specialty Cleric Advancement
Start with a normal undead-turning, no-spell-at-first-level cleric. All acolytes of all faiths operate exactly the same under this scheme (except for those badguy clerics who can Cause Light Wounds and Recruit Undead). Advance hit points, to-hits, saves, and turn undead normally. For each new spell slot you would normally gain, roll on the following chart instead.
01-05 You gain +1 to hit instead.
06-15 You gain +1 on all saves instead.
16-62 You gain a spell slot as normal.
63-64 Your ability to Turn Undead increases by one level.
65-67 You gain the ability to convert one memorized spell per day into [1st level cleric spell]. If you don’t have any spell slots yet then you gain that spell as a daily power. If you roll this again, you can convert as many spells as you want into [1st level cleric spell] (or you gain 3 per day usages, if you still have no spell slots). Reroll this result after that.
68 When standing at [location] you feel the power of your god flow through you. Make a Wis check every time you cast a spell there. If you succeed, you do not lose the memorized spell. If you roll a “1” you channel too much divine energy and take 1d6 damage for each level of the spell. Reroll if you get this result again.
69-71 You gain the ability to [Lesser Miracle]. Roll again if you get this result a second time.
72 You gain the ability to [Greater Miracle]. Roll again if you get this result a second time.
73-74 You get better at wielding a [weapon]. If you are not proficient with this weapon already, you gain proficiency with it. Otherwise, you gain +1 to hit and +1 damage with that weapon each time you roll this result.
75-77 You can turn [enemy] once per day, using the nearest equivalent hit dice undead on the Turn chart. If you get this result again, your ability to turn that kind of creature goes up to 3x per day. On a third roll, you can make as many attempts to turn [enemy] as your level (min 3). Reroll this result after that. Note that this ability is always standard Turning Away, even if you are one of those badguy clerics who normally Recruit Undead.
78 Fanatical Followers: Any henchmen or hirelings you obtain who do not already have a strongly documented faith gain +2 morale from your contagious religious fervor. Reroll if you get this result again.
79-80 You gain the knowledge of [basic lore]. The DM may require an Int roll to take advantage of this. On a second roll of this result, you gain the knowledge of [secret lore]. Reroll if this comes up a third time.
81 No more than once per session (sometimes it may not be practical) you can perform [ritual activity] and immediately refill your empty spell slots. Reroll if you get this result again.
82 When holding aloft a [object] dedicated to your god (which you can achieve with a simple bless spell), all attempts at turning are at +1 on the turn and number/hitdice turned rolls. If you roll this a second time, the hallowed object also functions in your hands as a bludgeon against [enemy], magically +2 to-hit and doing 2d6 damage, but there is a 50% chance at the end of the combat that the object falls to pieces. Roll again on the third or subsequent occurrence of this result.
83 Declare a Crusade: Pick a single species of monster or other type of foe that really cheeses you off. You cannot select [ally], [class], or [servitor], though you can declare a crusade against a group that a minority of these might belong to. All your party members are +1 to hit and damage against your declared foe so long as you are standing with them. If you choose [enemy], the bonus becomes +2. This works up to and including massive army scales. You do not get the bonus. If you get this again you must declare a new crusade against someone else. The old bonus no longer applies.
84 The mere sight the mark of your god fills you with hope. Once per session when you happen across [color or symbol] in the course of play (i.e. you can’t stage it), you can either regain a single used spell slot or heal yourself of 2d6 damage.
85 When wearing [clothing] you are +2 on all saving throws. A second roll makes you +4 and a third +6. Reroll after that.
86 You gain a pet [animal]. On a second roll of this result, you gain the ability to communicate with any [animal] as well as any monster similar to it. On a third such roll you may attempt to charm any [animal] or any monster similar to it once per day. Reroll after that.
87 Once per day you can channel the power of your god into a burst of pure [element]. It does 2d6 damage to one target, no to-hit roll needed, at a range of up to 60’. For each memorized spell you burn, you can add 1d6 damage or add another target adjacent to the first. Only those diametrically and cosmically opposed to your god are allowed a save for half damage. Among mortals, only enemy cleric and (anti)paladin types normally qualify for a save.
88 Pilgrimage: The thing you seek, the MacGuffin or whatever, is located in the tomb of a saint nor more than 4 play sessions away. You must have a fair shot at it--like any other treasure, but there's no guarantee you will get it. If you don't get it by the fourth session you can keep trying or let it go and roll again on this table. However if you choose to roll again and then you do get the thing somehow anyway, you lose whatever gimmick you rolled. The DM must think up some clever reason why.
89 Holy Consumables. You may begin each adventure with [food] imbued with the power of any first level cleric spell of your choice. Whoever ingests it can use the power of the spell. You have as many portions as your current level. If you roll this again you may select a second level spell instead, etc.
90 You get +2 saves versus [element]. A second roll of this grants you the ability to take no damage when a successful save results in half. A third roll make save-for-half situations into save-for-none/take half damage if the save fails. Reroll fourth or subsequent occurrences of this result.
91 If you personally witness someone violating your faith’s taboo of [taboo], you are +2 to-hit them in melee and they are -2 to save against any spells you throw at them. However, if you witness party members or other allies doing the same thing then your cure spells will no longer work on them. Reroll if you get this result again.
92 Future Saint: The site of your death becomes holy to your faith. No [enemy] may enter there and fellow adherents who rest here regain spells in half the usual time. Oddly, this still applies if you are resurrected or raised (don't tell the pilgrims). Reroll if you get this result again.
93 You gain a spell slot as usual AND a bonus slot of the level below it. If you were rolling for a first level slot, you gain two first level slots.
94 Timing is everything. When it is [time], your spells take effect as if you were 2 levels higher or you get +2 on dice (such as Cure Light Wounds).
95-96 You gain an acolyte (1st level cleric) as a free henchweenie.
97 You gain a spell slot one level higher than you were rolling for! However, if you ever violate your faith’s taboo of [taboo], you lose that spell slot forever.
98 The next time you find a magic [weapon] or [object] of unspecified provenance you can declare it a minor relic of your faith. Any cleric or adherent of your faith can use it, despite class or other restrictions. Furthermore, roll once on a random potions chart. In the hands of a cleric of your faith, it has that potion ability as a daily power. Work out with your DM how bad potions like poison or delusion work to the benefit of the user.
99 Roll on the chart for the [class] class. If that chart does not yet exist, roll on something similar (e.g. use the Thief chart if directed to a non-existent Assassin chart) OR roll on the Miscellaneous chart.
100 When you are really in the soup you can call on a [servitor] to help you. It will perform one service on your behalf, subject to DM interpretation, or join in a single combat. You can call on the creature but once. Reroll if you get this result again and have not summoned the servitor. (I.e. you can't bank more than one divine bail-out.)