If you're looking for a DNS host I can definitely recommend Amazon's Route 53
Thanks guys, it turned out to be down at least a couple of days but I think it only impacted my ability to make changes as I was still receiving mail. Think they get hit by ddos from time to time. Anyway, it's been OK since, to the best of my knowledge.
Not heard of OpenDNS or CloudFlare but will take a look at some point if I need to change.
Would probably also consider freedns.afraid.org.
Cloudflare are a CDN that specialise in DDOS protection, as part of this they will host your DNS. They have a free level service with minimal functionality, but you can delegate your DNS to them and they are excellent. I haven't had a tick of downtime across multiple domains in 2 years with them and the webui is easy to use. You get free analytics if you want to turn that on also. I use these guys for my top level DNS and then delegate subdomains to Amazon. The Amazon part costs me like 60p a month or something.