I use lunarpages.com , thye have a flat fee and dont add other fees such as ICANN fee like GoDaddy do, and they have great hosting too!
Been using Regfly since 2001 myself, but started using NameCheap recently and it seems easier to use. It is easy to find valid vouchers for it as well. A quick Google search and I could shave off almost two dollars when registering the first domain name with NameCheap. I have no experience with their customer support as I have not required it yet. Setting up DNS and all that was easy also. Another reason I chose NameCheap is free transfer of domains to other users.