Don't use water, including cleaners that contain water, because with some keyboard designs the water can remain trapped for days and cause corrosion. This is especially true of keyboards that use a rubber membrane or foam-backed foil pads for the key switches. Instead use electronics spray cleaner, which will evaporate completely and won't harm plastics. CRC Electronics Parts Cleaner ($4/11 oz, auto parts and hardware stores) and Radio Shack Cleaner/Degreaser ($8/6 oz) are suitable products. Alcohol is also safe, rovided it's at least 90% pure. Regular 70% alcohol contains too much water.