There are several companies that offer reseller accounts. Some of the ones to consider would be: eNom, WildWestDomains, Directi and OnlineNIC. I'm going to let you do a search on each of those to see what you think, because everybody has different tastes and needs in domain names.
Personally, I really love my eNom reseller account. It has all the bells and whistles that customers seem to like and it has a nice stable system that I like. It's not a perfect company, but I also like that when the customer goes to eNom, it is not readily apparent what I am paying for the domain. Instead, it appears that eNom charges $29.95 retail for each domain. The other registrars make it easier for end users to find out my wholesale price.
As far as automation, I would recommend www.DramSystem.com
and their Drams Plus which would allow for domain registration and hosting sign-up.
Drams used to come with a free $7.95 eNom reseller account... I don't really know if they still do that. If not, you could sign-up with www.NameZoom.net
for a free eNom reseller account.