(listed in no particular order)

PUZZLE WORLD http://johnrausch.com/PuzzleWorld/default.htm

THE IBM BURR PUZZLES SITE http://www.research.ibm.com/BurrPuzzles/index.html

PUZZLE MUSEUM http://puzzlemuseum.com/

ROB'S PUZZLE PAGES ARCHIVES http://www.rfh.dds.nl/puzzle_page.html

MARTIN WATSON'S MECHANICAL PUZZLES http://www.martinhwatson.co.uk/puzzles.html

GATHERING FOR GARDNER - http://www.g4g4.com/

WITFUL NET http://witful.net/

JUNO'S WORLD Junichi Yananose http://www.polyhedra.jp/zindex.html
JUERGEN KOELLER'S BURR PAGE http://www.mathematische-basteleien.de/devilsknot.htm
TREVOR WOOD T.W.PUZZLES http://www.puzzles.force9.co.uk/index.htm
PACIFIC PUZZLEWORKS http://www.pacificpuzzleworks.com/
MATTI LINKOLA http://www.tutka.net/~linkola/index.html
PER MOLLER NIELSEN http://www.mypuzzle.dk/
RICHTER'S ANCHOR STONE BUILDING SETS http://www.ankerstein.org/
PUZZLE & GAMES RESOURCES - directory of Puzzle Games related websites. http://www.the-games-hub.com/Puzzles/

PUZZLE IT Romania - http://www.puzzle.ro
PUZZLE IN (in Japanese) - http://www.puzzlein.com/
ALL MY PUZZLES A collection of puzzles - http://home.comcast.net/~l-whiting/attbi/HOME.html
LEONID MOCHALOV Puzzles of Leonid Mochalov - http://www.puzzlemochalovlp.com/
JERRY SLOCUM PUZZLES OLD & NEW - http://www.SlocumPuzzles.com
Sam Loyd puzzles - http://www.samuelloyd.com/
The Jerry Slocum Mechanical Puzzle Collection - http://webapp1.dlib.indiana.edu/slocum/
Martin Gardner (October 21, 1914 – May 22, 2010) - http://en.wikipedia.org/wiki/Martin_Gardner

ARIE BREDERODE - http://members.home.nl/arie.brederode/
PUZZLEUM - http://www.puzzleum.de/

LES CASSE-TETE DE CHANTAL (in French) - http://collection.cassetete.free.fr

PUZZLESOLVER http://www.puzzlesolver.com/
GAMES & PUZZLES REFERENCE CENTRE http://www.gamesandpuzzles.co.uk/reference/solutions.htm
PASSION FOR PUZZLES http://www.passionforpuzzles.com/collection/
PUZZLES WILL BE PLAYED http://www.asahi-net.or.jp/~rh5k-isn/Puzzle/
JAAP'S PUZZLE PAGES http://www.geocities.com/jaapsch/puzzles/
Puzzle Fun Magazine Archives http://www.puzzlefun.com.ar/

Every position of Rubik's Cube™ can be solved in twenty moves or less. http://www.cube20.org/

Play with Interlocking puzzles online. http://armorgames.com/play/10591/interlocked

Classical Chinese Puzzles. Photos and histories of traditional Chinese puzzles. http://chinesepuzzles.org/