I used to use IYD.com and was happy with them, but ever since they were sold out to Tucows, simple things like registering a nameserver have become nightmares. They're presently operated as "Hover," which appears to be owned by OpenSRS. The Hover control panel has very little functionality, so routine changes require tickets, which were taking five days or more to be addressed the last time I submitted one.
Another thing that irked me was that I had been a reseller for IYD. Before they were sold, things like password resets for customers who forgot their passwords were easy. Once Hover took over, I lost the functionality to resolve problems like that; but Tucows, OpenSRS, and Hover continued to tell clients that they had to contact me to resolve these issues, despite admitting to me that I had no way of doing so other than submitting a ticket.
So I decided it was time for a change. I'd heard of GoDaddy, of course (as well as most of the other big names in the game), but I decided on GoDaddy based on Jesse's experience and recommendation.
One thing that impressed me about GoDaddy was when I got a personal phone call from a real, live person the day after I moved the first five or ten domains over, welcoming me to the company and asking if I had any questions. That was a nice touch.
-Rich