Archimedes' Laboratory [ http://www.archimedes-lab.org/ ]
Play, create or solve intriguing puzzles; tackle tricky math problems; and discover new optical illusions.

Puzzle Depot [ http://www.puzzledepot.com/ ]
Devoted to puzzles, board games, trivia contests, shockwave games, puzzle books and software. Test your brain on crosswords, riddles, word puzzles, logic games, strategy and board games, a large selection of shareware links, and shockwave arcade games with lots of action.