Ask HN: What's the best domain name / DNS management portal?

Hey guys,

I'm looking for a portal where I can hold our internal domains as well as the domains of our clients. The service would need to have a decent DNS system in place, and allow easy management of domains renewals, etc.

Specifically (and here's the tricky bit) we'd like to be able to 'group' our domains by client, possibly allowing for separate invoicing or payment details, but not a necessity.

Does anyone have any suggestions?

Thanks!