You can use a damp cloth, just be careful around the buttons. water or soap-and-water will do the trick, don't use any harsh abbrasives. In terms of cleaning the scroll pad (gets very dirty from oils on your fingers) use a coton ball and rubbing alcohol.
I purchased the iCleaner solution, and i have to say it works really well. Makes the metal back glisten, and it got a few scratches and some water marks off the white parts and the screen.