There is a very interesting variant using playing cards instead of d20s. Take a deck, pull out all the face cards, aces = 1, black suits = 10 + card value, and deal 5 cards to each player, and the DM gets 8 or so. Instead of rolling 20s, you play a card, applying all the normal D&D modifiers. The players get to choose when to use each card; when they've used up all 5 they are dealt 5 more.I like this idea, though I know some folks won't. I'd want to keep the face cards and jokers and come up with something jazzy for them to do. The other problem would be players trying to work the system by initiating non-dangerous but roll-requiring actions in hope of dumping their low cards.
This would be a nice mechanic in a story driven game. Task resolution is still random, the math stays the same with the same success/failure probabilities, but players have a lot more control over when they "roll well" or "roll badly."
Anyway, if you're intertested in the Advanced GMG it's not yet available in print but RPGnow has it in PDF form.