I currently am running my hosting business off of a single VPS in Spry's Seattle datacenter by VPSLink. I picked up this week some local small businesses who host their own exchange and need very high reliability DNS for their mail. I would prefer to automate it and since my VPS runs cPanel, I figure my best solution is cPanel DNS only. I have done a little research, but can't find any killer offerings.
$80USD a year from envisage technologies in austrialia offering 4 independant servers, 2 in Australia, 1 in Dallas, 1 in Chicago. Drawback here is I am having a hard time getting responses from their sales team so I am afraid the service might be lousy.
$6.62 a month for a VPS from VPSLink in their new East Coast datacenter. (My main server is from them in Seattle) This would be self managed on my part, but it can't be that bad since it is DNS only.