• John Rausch site

A must! In my opinion the best site devoted to puzzles. It contains an on-line version of Coffin's book "The Puzzling World of Polyhedral Dissections", wich you must read in you plan to understand or make puzzles. It also hosts Nick Baxter's 'Sliding Blocks Puzzle Page'. It is the biggest recopilation in this category I know and you can play many of them with a very good applet.

There is also a forum available for puzzlers and information about the IPP (International Puzzle Party) Puzzle Design Competition.

• The Slocum Puzzle Foundation

Jerry Slocum has one the biggest puzzle collection in the world. He also sells some books on puzzles.

• Puzzle will be played..

Tons of information about puzzle design and solutions. Mainly Put-Together and Interlocking. Managed by Keiichiro Ishino. Much content is in japanese but there are lot of graphics.

• 3D Puzzles

Desings collected by Peter Caldeway.

• Peter Knoppers Puzzle Collection and software

Peter shows his collection, like me, and has a program in C-languaje that at some time I used to solve Put-Together puzzles.

Eric Fuller's collection and art. Nice photos. Easy navigation.

Nice interlocking and disentaglement puzzles. e-Shop available for his puzzles (Jose W. Diaz) and for another crafters. 

• Mathpuzzle

Managed by Ed Peg Jr. A good site to be up to date in puzzles. Mainly mathematical, packings and tiling are very frecuent.

• The Poly pages

Devoted to polyforms. Tons of information.

• IBM Burr Puzzle Research Page

All you need to know about the 6 Piece Burr Puzzle. Includes a wonderful Java applet that lets you to design your own 6 piece burr. Developed by Jürg von Kamel.

• David Winkler's Burr Puzzle Site

Smaller than Kamel´s but a worth also.

• Nick Baxter Sliding Puzzle Page

Hosted by John Rausch, the more comprehensive list I've found so far on the net about this type of puzzles.

• Hirofumi Jujiwara's Homepage

A nice collection of Java sliding piece puzzles.

• Izumiya

Wonderful japanese puzzle boxex.

•  Rick Irby Puzzles

Puzzles or jewels?

• Livewire Puzzles

Another worderful set of puzzles.

• Tucker-Jones House Inc.

Wire puzzles with an old fashioned look.

• Rob's Puzzle pages archive

Very long list of links to sites related to puzzles by Rob Hegge.

• The Genel Collection

Special interlocking puzzles.

• Trevor Wood's web site

Puzzles designed by Trevor himself and other by Coffin, Yoshigahara and others. Very nice crafted. I did't still saw boxes and trays better than Tervor's.

• Trevor Wood Puzzle Site

His crafts are unique

• Bill Cutler Puzzles

One on the most prolific designers

• World of Wooden Puzzles

Nice place by Jürg and Karin von Känel.

• Juno's Puzzles

Puzzles by Junichi Yananose. Both in English and Japanese.

• Interlocking Puzzles

Wayne Daniels puzzles are of great quality and very nice and difficult.

• Agon

Some nice applet games.

• CWC Puzzles

• Puzzlesolver3D

A very good program to test and design 3D interlocking puzzles based on unit cubes. I managed to transform other puzzles to equivalent usable by this program. I also use it for some packing puzzles. Made by the Andre van Kamen.

• Adrian Fisher Mazes

• Cleverwood

Interlocking,  Put-Together, Japanese Puzzle Boxes...

Also creations from the owner. Nice place. 

• Kadon Enterprises

Sell sets of polyominoes, polyiamonds and polycubes.

• Nemmelgeb Murr Import Shop

A very special site: design is a pleasure. Polyforms and other (better see yourself). William Waite is the owner.

• Binary Arts

• Bits & Pieces

• Karakuri Creation Group

Group of Japanese craftsmen specializing in trick opening boxes.

• Pacific Puzzleworks

Interlocking puzzles with great precision and a wonderful finish.

• Mr. Puzzle

Very good puzzles from Australia by Brian Young

• PULS

Number puzzles online.

• Puzzle Palace

Moooore puzzles on line.

• Conceptis logic puzzles

Puzzles online.