I came to W2COG website because it was referenced in an article in the Communications of the ACM on using agile software methods for government projects. They did an experiment where two projects were to produce similar software. One project used the "standard" procedures, spent $1.5 million, and only produced a document. The other project used agile methods, spent $100k, and produced working software.
They've published some information on using agile in government projects. Go to their website and click the publications link. I would provide a link, but it's one of the worst uses of flash for a website that I've seen (see previous post).
Update: Changed some of the sentences around and did away with worst website moniker. I've seen much worse sites. I was frustrated so I was harsh.