1 and 1.com sells domains for $8.99. They have frequent specials at $6.99 and every once in a while they will give the first year free.
I get good deals with godaddy, there's a coupon right now for $6.89 for .com ! if you go on domainnamehut.com and click on the godaddybanner it applies the coupon. there's no actual coupon code it has to be clicked to be applied so sorry, this is my website btw, domainnamehut. Anyways, even without the coupon I think godaddy is the best and cheapest in most cases.
GoDaaddy have quite an aggressive policy towards domains which they consider non-socially useful! For example they have a policy of suspending pharmacy and some xxx domains. If this doesn't affect you then by all means use them. Personlly I have always been happy with mydomain..com or dotster.com (owned by the same company), who do .coms for $9.95/year, so a bit more expensive, but the control panel is more user frienndly than goDaddy's. Good luck anyway!
Name.com is pretty good. Their domains aren't expensive, they have free private whois and they have good support incase you have any questions. I recommend it!
I have my own coupons for that.. I can provide at 3$ per domain, for bulk orders. You can try if you want.
godaddy are good on pricing e.g. lots of .info for 89 cents. Register your name and then point towards hostgator.
I suppose diffrent domain name registrars can have diffrent prices for the domain name registration for various domain name zones.
I think all place that you register your domain is the same,.. except you got some voucher or coupon code that give you a half price..
just research. i am sure every domain registrar has their domains reg prices right smack in the faces of the site visitors so you pricing research would be easier.