Accounting and book-keeping, once money starts to flow.
Payroll.
Support (you'll want it taken care of, but you shouldn't succumb to the impulse--at least not entirely, because you need to support customers daily in order to understand them).
Legal crap. Taxes, employment agreements, etc.
I want to say billing and invoicing and payment handling, but I think it's probably more efficient to bite the bullet and integrate these tightly into your own system--so that you always know exactly what's happening and how every change in your product or marketing effects your bottom line.
Payroll.
Support (you'll want it taken care of, but you shouldn't succumb to the impulse--at least not entirely, because you need to support customers daily in order to understand them).
Legal crap. Taxes, employment agreements, etc.
I want to say billing and invoicing and payment handling, but I think it's probably more efficient to bite the bullet and integrate these tightly into your own system--so that you always know exactly what's happening and how every change in your product or marketing effects your bottom line.