VirtualCube 3x3x3 - Learn to solve Rubik's cube by learning 3 simple tricks. - http://www.ganpuzzle.com/vcube333.htm
The K-Ball - 3D logic puzzle featuring 3, 8, and 26 segment versions. Requires Flash. - http://www.sphere-mania.com/
Rubik's Puzzles - A collection of puzzles by Erno Rubik, creator of the Rubik's Cube. - http://www.dotsphinx.com/rubik/
Rubik's Cube Java Applet - Scramble the colours then try to right them again. With mirrors to see the back of your cube this modern classic puzzle works very well on the web. - http://www.schubart.net/rc/
Livecube - Puzzle with millions of combinations. Requires Flash. - http://www.livecube.com/
Twisty Puzzles - All kinds of odd shapes of 3D puzzles in addition to the usual cubes. - http://byrden.com/puzzles/