I don't like to slow down the game by flipping through rulebooks - that's why I made the Monster Manual on a Business Card and various other rules minifications. Here's a treasure-generation rule that I made up recently when I didn't have a DMG with me.
Flip for Coins
You shouldn't roll dice to determine how many coins you find: you should flip coins. When the DM announces that you've found treasure, everyone digs into their pocket for loose change. Each player generates a little piece of the treasure haul.
Each player flips a coin. On a heads, you find 100 copper pieces. Keep flipping. Every time you get a heads, the coins increase by one denomination (copper to silver to gold to platinum). The first time you flip tails, you're done: you walk away with your treasure.
The average amount of money generated with this system is something around 40 GP per player, with a 6% chance of getting the maximum value of 100 platinum. With five players, your expected money value comes within a few GP of the average treasure generated by using the treasure chart from the DMG random dungeon generator (and Dungeon Robber). If you want, you can scale the treasure the same way Gary Gygax does: multiply the number of coins by the dungeon level. Thus, on level 3, each treasure is made up of 300, instead 100, coins.
To make the experience as close as possible to the greedy act of pawing through coins, use a penny for the first (copper) coin flip, a nickel for the silver flip, a dime for the gold flip, and a quarter for the platinum flip.
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Roll for Gems
We flipped coins for coin treasure; but the closest D&D analogue for gems is multifaceted dice. The original OD&D rules use a d6 for determining gem value, and I think we should continue that tradition.
Each player should roll a d6 (preferably a translucent or sparkly die, or even a semiprecious stone die).
First, roll a d6 to see if you found gems. on a 1-5, you find nothing. On a 6, you find the least valuable (10 GP) gems.
If you found a gem, roll on this easily-memorizable d6 chart:
1-5: You're done!
6: Multiply gem value by 10, roll again.
According to my calculations, the average value for this exploding die roll, with a maximum gem value of 100,000, is about 20 GP.
When my group played with these rules, the party found a smattering of ordinary treasure and one improbably giant sapphire worth 10,000 GP (the odds of a hoard holding such a gem in a five-player group: 400 to 1). I like the swinginess of these treasure rules, for the same reason that I like the swinginess of the original OD&D treasure charts, which also generate the odd 10k gem.