Click'N Slide
Flash version with downloads for Windows and Mac. Has several different pictures and allows you to choose the size of the grid.
Puzz
Sliding block puzzles for Amiga that can have non-rectangular puzzles and L-shaped pieces.
Slide "M" Puzzle
M&Ms themed version for the Mac.
WarpGear's Slide Puzzle
Slide the blocks around in the frame to put the picture together. (Windows)