It depends on what you're looking for:
http://www.chesskidantics.com/chesspuzzles.html
http://homepage.ntlworld.com/adam.bozon/ChessPuzzles.htm
http://www.princeton.edu/~jedwards/cif/intro.html
http://www.chesskit.com/training/
http://jeremysilman.com/
Have fun
IvanH