I just got done using Stoner's Invisible Glass and it works pretty good. It comes in a spray can and costs around $4.00 at Wal-Mart.
Another useful item is the "Glass Wizard" window cleaning tool. It is one of those "as seen on TV" products, but it actually works. It has a Microfiber net and it really helps you to clean in those hard to reach areas. I bought mine at Walgreens for about $10.00.
I noticed that after I cleaned the windows there seems to be some lint left behind. A quick wipe with a microfiber towel (not cotton) seems to pick up most of the lint. After that the windows look really nice!
Whatever you do, do not use the "glass cleaner wipes" that you find at Wal-Mart, K-Mart, etc. All they seem to do is spread around grime and leave streaks behind.