gigeservers has
http://www.ddosprotection.com/ - Which, while I have no personal experience with, is supposed to be rather good. All it takes is pointing your DNS at them, and you're good to go. I figure that if it's anything like their inhouse ProxyShield system, it might be rather pricy.
I'm not sure how redundant this would be if your datacenter already has good dos protection, but if they're still getting through, it might be worth talking with the ddosprotection people.