In reply to John Spade.

Thanks John!! As for recommendations, I think it depends on the size of the attack. Prolexic is one of the best out there, but may be too "big" for their needs. There are lots of little ones out there, like DOSarrest and Neustar that I have had success with in the past. Some large ISP's offer these services too, like Verizon. If you have a single provider, this may be an option too.
As for how to find the best one, I tend to look at their customers, and what types of attacks they have protected against in the past. I also tend to see if the vendor puts out whitepapers and such on past/present attacks and future trends. This way I know they are doing their due diligence. Hope that helps!!