Have you seen Esther Schindler's great article yet? Creating High-Performance Virtual Teams of Freelancers and Contractors.
Here's the blurb:
Plenty has been written about telecommuting for employees: how to encourage productivity, build a sense of “we’re all in this together,” and the logistics (such as tools and business processes) that streamline a telework lifestyle. But what about when your team is neither employees nor on-site? That gives any project manager extra challenges.
Lots of good tips.