Lots of issues to consider beyond price. Go with a US based registrar if you are in the US as you will be governed by their laws with regard to disputes or jurisdiction issues. Some will hit you with hefty RGP (redemption grace period) fees if you miss the renewal date. Domain theft is a becoming a huge issue, so finding a good registrar can be very important for your business.
Moniker.com and NameCheap.com are the best in my opinion with Demand Media's eNom right behind them.