I have 150 domains with Registerfly.com and its very stable with very nice control panel.
Namecheap and Godaddy are also big names with almost similar prices.
█ IndoUS HostingQuality IT Services since 2004
█ Shared Hosting • Reseller Hosting • Dedicated Servers • Domain Names
█ Custom Web Development • Mobile Application Development • SEO
█ Custom E-Commerce Solutions, Sports Portals, Health Care - Health Tourism Portals
I had been generally pleased with registerfly until recently a problem occurred. After almost two weeks, the problem is still just partialy solved. It took their technical support stuff a long time to answer tickets, and the quality of responses I got wasn't always good. So I wouldn't recommend registerfly (unless all you want is to register domains but don't intend to actually use them...).