Pentomino - Pentomino information, puzzles, problems, and exercises.

Sam Loyd - Info about Sam Loyd and his puzzles. Download his "Cyclopedia of 5000 Puzzles".

Treasure Hunt - Play for free, solve the cryptic clues and win cash prizes.

Web Riddle - Get to progressively more difficult levels through URL manipulation.

AgeOfPuzzles.com - Interactive and printable puzzles, plus lots of puzzle links and resources.

Nick's Mathematical Puzzles - Math puzzles with hints, answers, and fully worked solutions.

pzzls - Logic puzzles, puzzling riddles and math puzzles.

Number Logic - Free daily Sudoku puzzles. Play online or print them.

Terry Stickels.com - Official website of puzzle author and speaker Terry Stickels.

Aha! Puzzles - Original creative puzzles, books, and tests designed by Lloyd King.

Barry R. Clarke - Liar problems, number conundrums, matchstick puzzles, lateral mind-benders.

MysteryPhotos.com - Identify the objects in the photos and win weekly prizes.

Braingle - User submitted and ranked brain teaser, mind puzzles and riddles.

The Contest Center - Puzzles, Riddles, and Contests for cash.

IQ Test - IQ, Aptitude & Personality Tests.

curiouser.co.uk - Paradoxes, puzzles, games, illusions, poetry, curious facts, quotations.

Puzzles.com - A great resource for Puzzles, Illusions, Tricks, and other Fun on the internet.

Free Puzzles - Lots of puzzles: Logic, Math, Weight, Moves, Geometry...

Mathpuzzle.com - Ed Pegg Jr's wonderful site full of math puzzles and mathematical recreations.

Lateral Puzzles - A forum for fans of lateral thinking puzzles.

Puzz.com - IQ tests, puzzles, games, trivia, freebies, & contests for prizes.

BrainBashers - A matabooboo of logic puzzles, math puzzles, language puzzles and paradoxes.

Archimedes' Laboratory - Hands-on thinking games which help teach mathematical applications.

thinks.com - Brain games. Free online daily jigsaw, crossword, and word search puzzles.

The Ultimate Puzzle Site - Basic & Math Puzzles, Brain-Teasers, Complex Problems.