Jim Loy's Puzzle Page  
   Classic and original puzzles.
   http://www.jimloy.com/puzz/puzz.htm

The Truth Tree's Math and Logic Board  
   Collection of math and logic puzzles ranging in levels of difficulty.
   http://www.truthtree.com/mathdoor.html

Dave's Logic Puzzles  
   Monthly logic puzzles with solving grids.
   http://members.aol.com/dfcurran/logic/logicpuz.html

IBM Research: Ponder This  
   Monthly logic and math puzzles set by IBM researchers with solutions.
   http://www.research.ibm.com/ponder/

TechInterview  
   Answers to technical interview questions, programming problems, and brain teasers.
   http://www.techinterview.org/

Perplexus  
   A forum and collection of brain teasers, logic problems, math problems, paradoxes, science games, probability, riddles, and geometric shapes. The puzzles are searchable and categorized, most have solutions.
   http://perplexus.info/

The Monty Hall Problem  
   A probability theory puzzle with solutions. [English and German.]
   http://www.remote.org/frederik/projects/ziege/

CrocoPuzzle  
   Contains print-out and interactive versions. [English and German.]
   http://www.croco-puzzle.com/en/

Mathematical Jigsaw Puzzles  
   Information on polyominos and square puzzles.
   http://home.hetnet.nl/~paslen/jigsawpuzzles.html

The Two-Envelope Paradox: A Complete Analysis?  
   Describes aspects of a critical problem and apparent paradox in probability theory.
   http://jamaica.u.arizona.edu/~chalmers/papers/envelope.html

WU Forums  
   Discussion board hosted at Berkeley with talk about a variety of solved and unsolved brain teasers.
   http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_hard

Tangram Magic Egg  
   Tangram which creates hundreds of birds including geometry, tasks, solutions and downloads.
   http://michael.bischoff.bei.t-online.de/index%20uk.htm

Two Envelope Paradox - Solution  
   Claims that the two envelope paradox comes from the incorrect use of probabilities.
   http://www.anc.ed.ac.uk/~amos/doubleswapsoln.html

Quick Logic Puzzles  
   Use the clues provided to deduce the correct sequence of numbers in the hidden code.
   http://www.robertwilliams.org/qlp/index.html

The Puzzles of Oscar  
   Contains puzzles and games with solutions.
   http://uk.geocities.com/oscarlagioia/riddles.html

Monty Hall Game  
   JavaScript example of the Monty Hall Game. This game demonstrates the real (empirical) affect of statistics. [Does not display correctly in all browsers.]
   http://montyhallgame.shawnolson.net/

Leisure Ideas: Puzzles  
   Some mathematical puzzles with answers and/or a hint.
   http://www.leisureideas.com/logic%20puzzles.htm

CellFighter  
   Shareware game based around an extension of the game of life.
   http://www.cellfighter.com/conways-life-download.html