I've got one of those. I didn't put it on my car though because when client sees my car and is paying $2000/mo for hosting sees you've got plans starting at $10/mo ($8 if you pre-pay for two years) it doesn't go over so well.
Please don't do mouse pads. For me, those are the most annoying prizes because the keyboard tray built onto my chair has a pad built in. T-shirts are ok.
If you wanted to get some nice stuff, find some kits like http://www.tigerdirect.com/applications/searchtools/search.asp?mnf=1583&cat=85 or just the pieces from each and have your logo stamped on them.