I found this great site for doing puzzles online.
http://chess.emrald.net/index.php
Basically you create a free account, and then the server keeps on giving you puzzles. It times you to see how fast you can finish them, and they give you a rating. I highly recommend this site for practice! There are a lot of people logged on at once, so you can see how well you solve puzzles compared to them.
Also today I created an account on www.chesshere.com which is a "turn based" chess server. It's basically correspondence chess. Right now I am playing 13 games at once on it. I think for most of the readers out there, www.chessclub.com is probably the best site for you, but if you like to play a slower correspondence game, I suggest www.chesshere.com.
