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

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/