Cube Slide Hexagonal variation on sliding tile puzzles. There must be two adjacent open spots to move a hexagon. http://www.24hours7days.com/Hexagons/index.html

Sliding Piece Puzzles Different sizes of pieces make these puzzles much more difficult than regular sliding puzzles. http://www.pro.or.jp/~fuji/java/puzzle/slide/index-eng.html

Books Online Cheap Puzzles Collection of online sliding puzzles featuring popular subjects including 'N Sync, Dragonball, Britney Spears, and Pokemon. http://www.booksonlinecheap.com/puzzles.shtml

Dance Puzzle Line drawings make these puzzles quite fiendish. You can reach the Hall of Fame if you're good enough. http://www.tdbs.is.nl/scripts/interactief/game/puzzel/index_EN.asp

9 Piece Puzzle Put together the Boston University logo (Java). http://scv.bu.edu/~aarondf/java/puzzle9.html

Pokémon Sliding Puzzle Game Fully customizable. You can select any of the 151 Pokemon as the image of the puzzle and customize any combination of 3-6 rows and columns. http://www.creatinghorizons.com/cgi-bin/slider.pl

Absolute Lines Challenging online puzzle game on a checkerboard. http://gameknot.com/lines.html

Mosaic Faces Celebrity online sliding puzzles offered at four difficulty levels. http://www.julienne.com/mosaichome.html

Boxcar Blockade A sliding box puzzle game with hundreds of challenging computer-generated levels. http://www.rhymezone.com/games/bb/

kibuR's Fifteen Double sided sliding puzzle. You cannot slide individual squares. Instead, you move squares by sliding rows and columns of squares at the same time. http://www.dotsphinx.com/games/rubik/fifteen/

OmniSlide Online slide puzzle which has no empty space. Instead, the pieces wrap around when the entire row or column is moved. Also available for download and placement on web pages. http://www.sapello.com/slidepuzzle/

Quazzle Online mixup puzzle game in which the object is to slide the pieces of each image to form a complete picture in the least amount of moves. Also offers a free downloadable screensaver. http://www.quazzle.com/

Nick Baxter's Sliding Block Puzzles Offers photos and a Java applet to play rare and collectable sliding block puzzle designs online. http://www.puzzleworld.org/SlidingBlockPuzzles/

Tim's Interactive Puzzle Solution Center Selection of online brainteaser and math puzzles. Includes difficulty ratings. http://www.sakharov.net/puzzle/