I have a few ideas.
Scareface Tony. This one is easy since I have a red shirt, just need to go to Goodwill and get a white suite. My friends Airsoft gun will work perfectly for my "little friend".
http://www.buycostumes.com/Scarface-Tony-Montana-Adult/20999/ProductDetail.aspx
30's Gangster with stripped suite.
http://www.buycostumes.com/Gangster-Suit-Long-Jacket-Adult-Costume/20065/ProductDetail.aspx
Or Mustang:
http://www.cosplaymagic.com/alun1.html
Or SG1, if I can get the stuff cheap enough at the surplus store.
Those jackets and vests are probably $$$$ though.
I was going to do a Castle Crasher, but I don't have the time to make it. I have two good Holloween party's to go to this year.