Akiyoshi's illusion pages - http://www.ritsumei.ac.jp/~akitaoka/index-e.html
Optical illusions and puzzle games by Akiyoshi Kitaoka. Gives information on each game and illusion.
Gamebetty - http://www.gamebetty.com/
Find a large collection of free online games and puzzle games that make you think.
MyPuzzle.org - http://mypuzzle.org/
Offers a home for puzzle fans. Sudoku, Jigsaw Puzzles and a lot of Brain Teasers can be found here.
Smiley Gamer - http://www.smileygamer.com/
Find free online flash games for girls, boys and kids. Also featuring puzzle, action, skill, sports, adventure, management and dress up games.
TopPuzzleGames.com - http://www.toppuzzlegames.com/
Play online flash puzzle games. Includes descriptions and game listings.