I have been compiling some sources of interesting, free worksheets. I have found a lot of dreck, and even the good sources really have to be filtered (this all makes me appreciate FlashKids etc. more). I will take time when I'm done and post what I've found, maybe converting this thread to a general free-worksheet thread.
In the meantime I thought this simple math maze generator was kind of neat, and that it might tempt some kids to memorize some math facts without becoming too bored in the process. You can restrict by difficulty and operation type:
http://www.worksheetworks.com/puzzles/math-maze.htmlETA: Haven't had time to go through it yet, but other parts of the site look cool too! I have just looked at the pentomino puzzle worksheet generator.