Browser Based

ADDiction
Solve each Java-based puzzle by swapping pairs of adjacent numbered tiles whose sum is a multiple of 3 or 5. Available for play online, or download.
http://www.geocities.com/TimesSquare/Labyrinth/2288/add/index.html

AOL Games - Puzzles
Offers online and downloadable puzzle games.
http://games.aol.com/browse-games/puzzle/

Blueee's Number Puzzle
Online game that displays a random choice of one of 15,000 different math puzzles. Six nested equations are shown with icons instead of digits. Find the digits to solve the puzzle.
http://www.tote-taste.de/X-Project/index.html

Brainwave
Determine the shape that doesn't fit in this series of ten visual logic puzzles. Solve all ten and get a top 5% brain award.
http://www.wognum.se/brainwave/

Caught At Work Productions
Offers a new brain teaser each Thursday, plus archive of past puzzles.
http://www.caughtatwork.net/

Celtic Solitaire
Online puzzle game in which the player must form lines of five or more color marbles to score points and enter the top 20 players list.
http://www.i-taneva.com/workshop/solitaire.html

Chockablock
Java game in which the player tries to score points by filling up 3 by 3 squares on a grid using tetris style pieces. Try to make the high scores list.
http://www.loquax.com/chockablock/

Clicker
Remove all of the black squares by toggling colors with each click.
http://www.apejet.org/sites/games/clicker.html

Colors
Try to line up five matching colored chips for removal, while the computer adds extra chips to the board randomly after every move. Use strategic skills to play for high score in this online Java puzzle.
http://www.geocities.com/SiliconValley/Park/5199/colors.html

CombinationLock.com
Select a numerical sequence based on clues. Has a hall of fame.
http://www.combinationlock.com/

Contamination
Take over the entire board by contaminating enemy pieces in this online Java game that combines strategy and puzzle elements. Play against the computer or up to two other players.
http://student.dei.uc.pt/~pamaro/puzzle.html

Cross Rings
Arrange the chain links in alphabetical order to solve this Java puzzle.
http://brightworld.com/CrossRingsPuzzle/

Cryptarithms
Features online brain teaser puzzles in which the digits of a sum are replaced with letters or other symbols. Find the correct numerical digits for each letter to solve the puzzle.
http://www.cut-the-knot.com/cryptarithms/st_crypto.html

Diamond 16 Puzzle
Rearrange rows, columns, and quadrants in a 4x4 array of 2-color squares to solve the puzzle and to make a variety of symmetric designs.
http://finitegeometry.org/sc/16/puzzle/

Dot 2 Dot 4 Fun
Online version of the classic Connect the Dots game. Offers a choice of pictures in categories that include people, buildings, and animals. Requires Shockwave plug-in.
http://www.dot2dot4fun.co.uk/

Dots and Boxes
Java applet playing at one of three levels of difficulty, with variable board size.
http://www.well.com/user/argv/java/dots.html

Facie!
A game about feelings and intuition, the object is to make Facie smile with the least moves possible. Playable on the Web or mobile phone, and includes the ability to create a game for others to play.
http://www.facie.com/

Hexcite
An online version of a board game where you try to place all your pieces a hexagonal board. Play against the computer.
http://www.hexcite.com

HopSkip
Move the red square along the game board to step on all the green squares and make them disappear. Create a new board or play on a board created by other players.
http://awe113.tripod.com/

JC Lava
Online game of logic in which players place pieces in rows and attempt to surround four of the opponent's pieces to win. Play is available for two players or one player against the computer.
http://jarci.w.interia.pl/

Jotto
Puzzle game in which the computer chooses a secret English word with five different letters. The object of the game is to use logic to try and guess that word through a process of elimination.
http://ourworld.compuserve.com/homepages/easysurf/menuj.htm

The Lateral Puzzles Forum
Set or solve lateral thinking puzzles. Includes a selection of current and already solved puzzles.
http://www.lateralpuzzles.com/

Lightsout Cube
An online version of Tiger Toy's Lightsout Cube and links to other Lightsout puzzle sites.
http://www.gersolutions.com/lightsout

Masterword
Try to guess the 4 letter word the computer is thinking of in no more than 10 tries.
http://www.masterword.co.uk

Misronet.com Puzzles
Offers free interactive logic puzzles including solutions and tips on how to solve brain teasers.
http://www.misronet.com/puzzles01.htm

NIM
Two player game in which players remove matchsticks in an attempt to force the other player to remove the last one. Played online against the computer or downloadable.
http://www.neil-mackenzie.com/nim/

Philosophy Games
A series of philosophical puzzles to challenge the mind.
http://www.philosophersnet.com/games/

PING
Maneuver balls into green chutes to score points in this online puzzle game that is a test of physics and strategy skills. Complete levels by rebounding a ball into eight chutes before time runs out.
http://www.smerc.com/ping/

The Problem Site
Solve math problems, brainteasers, word games and riddles. Featuring a selection of free puzzles to help develop problem solving and lateral thinking skills.
http://www.theproblemsite.com/

Quadrix
Click on squares to change the color of neighboring squares and bring the entire grid to one color in this JavaScript logic puzzle.
http://jumk.de/quadrix/quadrix_e.shtml

RiddleScape
A ranking and competition system based on a select number of puzzles.
http://www.riddlescape.com/

Rockz
Escape the caves with as many diamonds as possible, while avoiding falling rocks and flying creatures in this free Java game.
http://rockz.co.uk/

Rolling Cubes
Roll eight half black and half white cubes around a 3 by 3 grid until you have reversed the colors.
http://www.righto.com/java/rollingcubes.html

SameGame
Goal is to remove all color tiles from the field, by removing connected groups of the same color tiles.
http://www.yook.de/samegame/

SegPlay
Play to beat the clock in this online version of a paint-by-number puzzle in Java. Features a selection of categories and images.
http://www.segmation.com/SegPlayChoose.asp

Set Game
Online versions of Set and Quiddler mathematical and word card games. Features a daily puzzle and contest.
http://www.setgame.com/

Sokoban
Tidy up all the crates of mail.
http://www.pimpernel.com/sokoban/

The Stone
Information about the internet's mystery game, The Stone.
http://www.netfysh.com/thestone/

Tile Puzzler
Offering online Pentomino puzzles, Tetris style puzzles, and overlapping tile puzzles. Solve existing puzzles or create a new puzzle.
http://www.tile-puzzler.com/

Tilt Puzzles
Labyrinth maze game, tilt the board to place the squares on their targets.
http://www.clickmazes.com/newtilt/ixtilt.htm