Tracking Hash/sec of major pools and individual (solo) miners I'd like to get a list of the hash power of the major pools, solo miners, and if applicable undocumented hash networks.  How can I obtain this information?

If this information already exists, how did that site or service collect that information?
How about http://blockorigin.pfoe.be which aims to provide a reliable source of information by scraping pool web sites to see which pool claims ownership of each and every block (hence avoiding the problem that Peter Wuille mentions).

See https://bitcointalk.org/index.php?topic=78391.0 for discussion.