I generally use HT's method, except I use soap and water instead of rubbing alcohol. If you want to REALLY get'em clean, put the keys in a salad tosser filled with whatever cleaning solution you use and spin 'em until they get dizzy. Soap and water always works for me. Be careful, though, some keyboards are a lot harder to reassemble than others.

But, as Hex said, unless it's a wireless, you can usually pick one up for $10 or less... it's generally not worth the trouble to clean wired keyboards.

Water on a keyboard is perfectly safe, as it is for any electronic component (save for batteries and capacitors). The catch is that said component must be off when it gets wet, and fully dried before it is powered up again. It will never know the difference. Besides which, alcohol conducts electricity beter than water (afaik). If alcohol is safe, so is water. The only electronics that cannot get wet are those containing high-powered capacitors, such as monitors, amplifiers, and some radio recievers. The water can bridge them and discharge them. Water can also discharge lower charge capacitors and fry things like motherboards, but I have indeed cleaned motherboards with soap and water before. I just don't soak the whole thing, so the leads are never crossed. Generally, avoid anything with capacitors or batteries when using anything that conducts, including alcohol afaik. But you needn't worry about that on a keyboard.