I use Namecheap. The control panel is the best out of all of the registrars. Im paying around 9-10ish but it comes with a free SSL cert so that pays off. THe support is answered quickly No problem with any sort of problem at namecheap.
I have used eurodns and sibername domain registrars. Their services are quality and inexpensive plus they offer attractive discounts on them.
You can never go wrong with Godaddy! You can get a coupon code to get a .com for $7.68 for the first year and use it for renewal also. Their support is GREAT also. You can call that at anytime and they are there to help with whatever the problem may be! I wouldn't suggest any other registrar!
I also use Godaddy, like 321Hosted does, and I find it very reliable. It's not too expensive and the support is fantastic
i use WhoisXY.com to register domains. and the cost varies for each domains depending upon various features.