I agree with Neal, an addon to QuickBooks or Peachtree would be beneficial. While I'm no longer a freelancer, there is more to running a business than just invoicing. And it makes no sense to have to enter information twice if you did use an accounting program such as QuickBooks or Peachtree.

But these programs are not good at managing customer relationships, or dealing with recurring transactions, etc. I think an application that would allow for this, and perhaps intergrate with a website would be more resourceful than reinventing the wheel.