I use http://namecheap.com/, only $8.88 for a domain and I've had zero trouble with them - and it doesn't take a lot of time to register a domain O_o

Godaddy.

I've been buying from Yahoo!. Buying another one tommorow.

Name Cheap is great!

directnic

another vote for namecheap here... best I've used.

Mostly i use enom.com

onlinenic.com

I'm happy with http://namesdirect.com/

----edit
what the hell?!
$30 to register domain??? it used to be $9 or something
I renewed few domains few weeks ago with old price so I'm a bit confused with this new one

----edit2
well.. actually I think they transformed into http://www.mydomain.com/ but I still log in with namesdirect site and can renew for $8,50

dynadot.com ;)