I saw on Mr Saltwater Tank TV .com a couple weeks back that the best thing to clean your tank glass with is... RO/DI water. Yup just put it on a cloth and wipe it down. I've tried it and it works really well... no poison and its easy to get!
I was always under the impression that commecial cleaners such as windex have ammonia and other nasty chemicals, I just use a water wet paper towel then dry it off with another