* Peter Beckman:
I can highly recommend DNSmadeEasy.com. Inexpensive, Anycasted, always fast and reliable. Good for primary and/or secondary, IMO, though it is sage advice to use two different providers if you are super ultra serious about never being down.
Or put some of your DNS servers on the same connectivity as your main services. After all, DNS is not an end in itself for most people. Running some of the servers yourself makes sure those are available even if some other customer at your DNS provider is DoSed, taking the entire DNS provider out at the same time. (Speaking in general, not about specific cases.) And if you're the DoS target, ultra-resilient DNS will simply cause the attackers to pick some other weakness of your setup. IMHO, fate-sharing as a strategy for increasing availability is somewhat underrated.