I find that ressources on open source governance is pretty scarce on the Internet and it surprises me that there is no proper "initiative" or "think tank" to develop this idea.
Not saying it's easy, but if you want raw data, there is a lot out there.
FEC filings from the last few decades: http://www.fec.gov/data/
Bills and legislators: http://www.govtrack.us/
Lots of data, but hard to access: http://votesmart.org/
A nice tool/repository for extracting and sharing data: https://scraperwiki.com/
This is just the tip of the iceberg. I'd be happy to talk with anyone else about finding what they need.