If you have alot of domain names, you can get some attention and competative rates from Registrars - they want your business!
I use Domain Bank. Domain Bank charges $35/year for domains. Domain Bank also owns 123Domains.com, where they charge $14.95/yr (nice market strategy.)
I was using 123Domains for all my domains. Then found MyDomains at $8.50/yr. And I started transferring the domains over.
Boy was I suprised to get an email from DomainBank asking "please don't go" and offering me competative pricing!!!!
I negotiated $7.95/yr for domains through Domain Bank. Domain Bank doesn't charge for registrar lock or registrar-side DNS entries, they have alot of other nice features. And if you have a problem, you can CALL there and talk to a PERSON to talk to. I've been really happy with them, and ya gotta love when a company says "we want yoru business" like that.
So... I'm happy to refer them. I suggest that you give Domain Bank a call, tell them how many domains you have, and ask if they can give you competative pricing, Negotiate a yearly rate with them that you're happy with and go to town... I think you'll be happy with them!