If you run a wilden west game or something like Victorian-era Cthulhu, then you totally need to get a copy of Barkham Burroughs' Encyclopedia of Astounding Facts and Useful Information 1889. Not only is this baby one of the best oddball reference books I have ever seen, but it provides an interesting perspective on the aspirations of the middle class in late 19th century America. Want to flesh out a dude from back East? Here's a great place to start.
There's so much haphazardly crammed into these 148 pages, it's pretty much the Dungeon Masters Guide for magnificently mustachioed white anglo-saxon protestants. (Speaking of W.A.S.P. and cowboys, 'Blackie Lawless' would be a fabulous name for a bandito.)
Stuff you can easily swipe for your game:
Sample business letters (p26-27) - for capturing the proper tone when providing a lead to the PCs via correspondence
How to be handsome (p39-41) - dubious cosmetic advice to inflict on lady-type NPCs
How to make artificial gold (p43) - also how to tell the stuff is fake
Business law (p43-44) - i.e. ways to trick the PCs
Durability of a horse (p46) - practical numbers for hauling cargo
Certain Cure for Drunkeness (p47) - iron sulfate, magnesium, peppermint and nutmeg. Who knew?
Twenty Choice Dinner Menus (p49-50) - Invite the PCs to a fancy dinner party, roll 1d20
Value of Old American Coins (p51) - Treasure!
And the list goes on and on. There are lots of home remedies and recipes to puzzle over, some obviously incomplete (e.g. how long do you bake this cake?). I've made the pickled eggs several times, much to the chagrin of most of the folks I've foisted them upon. The "Themes for Debate" section gives a good sense of the concerns and goings-on of the day. The title of the last section is "Twenty Thousand Things Worth Knowing", which takes up all of 18 and a half pages.
Seriously, this is one of my all-time favorite books. It just oozes this lovely combination of audacity and quaintness. You remember how at the end of the 1960 film version of The Time Machine they notice that the protagonist took three books with him when he left to re-educate the Eloi? Barkham Burroughs' tome simply has to be one of the three. The universe wouldn't make sense otherwise.
"Man, is there anything Jeff CAN'T do when it comes to gaming? This guy is like a critical 20 every roll. Jeff can bite the heads offa five game geeks, including their sorry-ass DM, and spit 'em into a large duffel bag ONE AT A TIME!...that's just the kind of messed up bastard he is! You think yer a gamer, punk? Well..do ya? Jeff will depants your weasel-ass right in front of your grandma."