I'll second the mention of godaddy.com. I'm not sure that they are the best, but I have had no problems with them for the one domain of mine they handle.
In general, your registrar will not support dynamic IP updates. You are on the right track with dyndns.org, but in order to use your own domain name you will need to use their Custom DNS service (a $30 one time charge).
~bex0rs