I have one of these, and when I got it I learned how to solve them.  I kept it on my desk.  Then last week, one of the guys at work messed it up on me – and I realized I’d forgotten how to put them back.

Google knows everything, I swear.

There’s a great cheat sheet here. Basically, it asks you questions about where different colors are, and shows you how to put them back one piece at a time.

If you want to try it and don’t have a cube, I like the virtual cubes here. (Make sure you have the latest Java plugin installed first). There’s a couple different color variations too, and 2×2 and 4×4 cubes if you want to be ambitious.