I like iKlear, but like mentioned above, if you regularly use the cloth that came with your MB with a little bit of water, that's all you need.
NEVER use anything with ammonia- I'd recommend staying away from all glass cleaners. Perhaps the new glass screens on the MB's make it possible to use regular glass cleaner, but I'm going to stay away. For what it's worth, I used a "Laptop" cleaner I got from WalMart once and it definitely hurt my whitebook screen. I'll never buy something like that again.