I use and recommend Namecheap (I’m not affiliated), both from my past two years with them as a domain registrar and more recently with web hosting. Thanks for good prices, great service and support, and coupons.
Namecheap has been a credible alternative for some of the other more well-known registrars out there to date and I use them for everything in this field, as much as I can.
UPDATE: If you have an iOS device (iPhone, iPad, etc.), the Namecheap app offers a management system for the domains that you manage at Namecheap: search, register, renew, view transfers and even change DNS, all on the go.