For a few domains, DirectNIC seems pretty good.
For bulk domain holdings ... say over 100 domains, then I'd personally recommend BulkRegister (I have 670+ domains there) ... they charge a nominal membership fee, but it's well worth it in the longrun.
BulkRegister.com
http://www.bulkregister.com/
If you and or anyone else here choose to signup at BulkRegister, please feel free to enter my referral code shown below - copy and paste into signup form, where indicated, for additional benefits:
d0823ca93
Many folks, especially those with many 100s of domains, like Enom, but I'm a bit leery of their service ... folks with only a few domains seem to run into problems and unexpected fees ... like I personally, awhile back, had a domain expire by one day at Enom and they charged me $29 to renew it.
For a complete list of ICANN accredited registrars see:
http://www.internic.net/
Another place to check out is DNForum:
http://www.dnforum.com/
Ron