Right now I'm just using the DNS service Godaddy.com provides. I've used
www.zoneedit.com and
www.dnsexit.com in the past, both are very reliable. Only issue I have with ZoneEdit is their website being unreachable at times but their DNS servers are rock solid on the other hand. I can't really comment on DNSeXit.com, didn't use them for too long before switching to Godaddy's. Reason I switched over to Godaddy is so I would have everything in one place and since I colocated my server it has static IPs, so I didn't need dynamic DNS updates ability either.
