The taurine recommended above is for cramps, which may or may not wake you in the middle of the night, make you hobble around like an arthritic crocodile, and/or cause you to curse your deity of choice. If you get them, the cramps can occur in darned strange places, like toes, fingers, hips, calves, etc.
Taurine (lots of it in some energy drinks, like rockstar) and increased potassium intake (bananas, sweetpotatoes) really help. For acute attacks, massage and drinking lots of water sometimes help.