National Puzzle Day is coming up and in honor, we're doing a puzzle program at my library. Scouting around for helpful websites yesterday, I stumbled upon Jigzone. Pick one of the many pictures; choose how many pieces you'd like to put together and go! No registration required to start playing.
It's very easy to waste time here, I quickly became engrossed in fitting 48 piece puzzles together--I can do almost two in about 15 minutes.
Other features to note:
Easily create your own puzzle with your pictures
Embed in your blog
So here's one to get you started: