Word of warning: the following flash that I linked to is addictive.
It's called White Jigsaw. It's rumored that there's no end to it, but I've read on the comments section of a game review website that there's a 64x48 monster.
http://www.gamedesign.jp/flash/whitejigsaw/whitejigsaw.html
So, how far can you get?
If you do manage to get to the end, be sure to tell everyone how big the last puzzle is.