You need:

Glass - full of beer is more impressive - you are confident the dirty penny won't fall in and contaminate it.

Two Forks

Coin - dime is most difficult - work up to it from a quarter.

How:

Place two forks with tines flat together, lined up. Put coin in middle slot. Balance edge of coin on rim of glass. The handles of the forks will counter-balance if you have everything working just-so.

More fun:

Get your friends to attempt this after each pitcher. After the third I am usually laughing too hard to do the dime. The penny is usually still OK. You know it's bad when you're fishing the quarter out of the glass with the two forks.

Diagrams: