Rackspace customer service
I just opened a ticket asking Rackspace to make some changes to their DNS for me (rather than running my own DNS servers I let Rackspace do it).
Typical of Rackspace, my ticket was immediately acknowledged and 7 minutes after it was opened they had already made the requested changed, informed me, and closed the ticket. Rackspace is not the cheapest — in fact it’s probably the most expensive — but it is the best.