The Domain Mapping plugin works with Enom currently, and I know people have requested that it be expanded for other domain resellers.
I would like to officially request that ResellerClub be added to the list and given priority.
1. Because they're much cheaper than Enom, and they offer free Private Registration. Enom charges $6/domain/year.
2. Because they have a built-in API, so this should be very easy to do:
3. Because they're recommended by WHMCS:
Side note: I know WHMCS is not necessary for using the Domain Mapping plugin. But it lends credibility to my case, since the only two domain resellers they recommend are Enom and ResellerClub.