I'd like to capture basic analytics (page views, visitors, time on site, etc.) across all of the sites in our network while also allowing users to install the analytics software of their choice. The network contains sites on a subdomain of a primary domain, as well as custom domains.
What's the best analytics tool for this purpose? Ideally, it would be just one analytics tag that could be installed across an arbitrary number of domains and subdomains. I'd prefer not having to register each domain by hand.
Update 9/11: I've installed Quantcast for the time being, and I think it will do the trick, but a more full-featured tool would be awesome.