Another vote for NameCheap. Have had ~50 domains with them for nearly 5 years now, never a problem.
(Not to beat a dead horse, but back when we could see the karma numbers for comments, it was possible to visibly "second" an endorsement comment by upvoting it, instead of posting separate +1 comments like this one ...)
I especially love how easy it is to transfer domain names between NameCheap users. I had purchased a domain name once with my personal account. Then I created a company and wanted the domain to be officially owned by that entity and not me. So I created another NameCheap account for that company, then transferred it over very easily.
Of course, it's possible other registrars offer such a frictionless transfer process between account holders too. I've only used NameCheap for this and can say I was pleased with the results.