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. Slide "M" Puzzle
M&Ms themed version for the Mac. Puzz
Sliding block puzzles for Amiga that can have non-rectangular puzzles and L-shaped pieces. WarpGear's Slide Puzzle
Slide the blocks around in the frame to put the picture together. (Windows)