SaaS client portal for sharing files, invoicing, messaging?

[jaysan]

For lack of a better way to describe what I'm looking for:

Can anyone recommend a SaaS application that provides a secure client portal where a company and its clients can upload and share files, send messages, and that allows invoicing and online bill payment? Security is important as some files contain sensitive information, SSL required.

I feel like I'm sort of looking for a CRM or something, but not really; and it's almost like base camp, but not quite. Ideas?

[StalkerB]

Well, you basically just described Basecamp but you need something like FreshBooks - http://www.freshbooks.com/ - for the invoicing part.

Nothing I know of that does both parts though.

EDIT: Maybe you try something you host yourself with a wiki software or something like - http://www.activecollab.com/ - or - http://collab.ws/.

Basecamp alternatives - https://company.podio.com/ - http://www.zoho.com/projects/ - http://lighthouseapp.com/ - http://goplanapp.com/