GoDaddy
This is currently the largest register on the internet for domain names, at least at the time of writing. I have found them highly competitive, established (you want ‘established’ in case the economy gets soft again), and because of their size they can be very inexpensive. They offer private registration too in case you don’t want your particulars shared with the world and its internet rogues. They always inform me with plenty of time when a domain name needs renewing without fault…