Hmmm... let me see...
Ok, most games used to print GM screens on that horrid thin card that gets bent or just plain old destroyed really easily. Please consider doing the screen on the same type of card used for the cover of the core rulebook - Wizards of the Coast, Mongoose and White Wolf have all switched to that method recently, and the end result is really tough and sturdy, and it looks just great!
The front really needs art of course. The middle two panels need something central to the theme of the game. Perhaps a grisly crime scene with a number of hard-boiled detectives stood overlooking the evidence? In the background a crime scene photographer takes a photo of the body, and a CSI dusts for prints on an old television on the nearby dresser. The left panel needs the game logo in nice big letters, and both it and the right panel would look good with an identical pattern of some sort - the old Wraith: the Oblivion GM screen did this really well.
As for content, I strongly suggest against a table with weapon statistics. A GM that's taken the time to create an adventure generally has weapon stats written down wth his/her NPCs. I've always felt that weapon tables take up a huge amount of space, never get used and are generally a bit of a cop out on the part of publishers. Of course - that's just my opinon! Someone may well step in now and say how useful they find them.
Anyway, there's my 10 cents. Hope it helps - I plan to stick around the forum for a while!