I've used Meguiar's Swirl Remover (PN: M0916), a professional grade ultra fine polish made for paint. Just wait till you use it on your paintwork...incredible stuff.
I've polished both my own windscreen and those of a few freinds to "like new" condition. This stuff is soooo fine, you'll need a small palm orbital polisher, or you'll be there all day. It takes me about an hour to get a screen to new condition.
When using the orbital polisher, the screen should not get warm/hot (don't apply a lot of pressure). Use a mist sprayer with water in it to keep things cool.