I've been using hosted-projects.com. It doesn't meet your "free" criteria, but it was <$10/month. And:
- Customer Support is outstanding. First-response time is usually less than 1 hour. Recently I asked for a one-time export of my repository, and the request-to-delivery time was less than 2 hours!
- It includes Bugzilla or Trac so you can track and prioritize your development issues. I haven't played around with security controls, but you might even be able to give your clients logins so they can log and view issues themselves.
