Sunglass cloths and things of that nature work great. I have a microfiber cloth, and do not use any liqiud whatsoever. It will clean the glass without leaving any streaks.
Cyber is right on. Liquids, especially alcohol, can hurt the glass over time, let alone taking the chance of getting liquids inside the phones components.
Get a microfiber cloth (eyeglass or sunglass stores are the easiest place to find the) and simply wipe the glass with that.
Just my two cents...