My 'vote' would go to GoDaddy. I think right now you cna transfer a domain and get 1 year on reg for like 7.00 or very close to that. Also - if a domain is registered with GoDaddy it can be pushed to another GoDaddy account at to no charge
Most registars are free for internal pushs. If you want an external push from one registar to another registar for a fairly cheap price would be Godaddy or Namecheap. Godaddy will be an obvious first.