This information is available at speedcubing.com (I love copy paste features)
Here are indications for the number of moves to scramble. 3x3x3 cube: 25 moves, 4x4x4 cube: 40 moves, 5x5x5 cube: 60 moves, MegaMinx: 60 moves, Square-1: 40 moves, 2x2x2 cube: 25 moves, other puzzles: twice the maximum depth of the puzzle.
I usually add a couple more twists on top of that number especially with the 5x5x5 to make sure I didn't do a few defeating moves.
Check out the site, it's a good resource