OpenSecrets.org has a list of candidates, and promises to eventually tell you about finances, spending and background.
The Federal Election Commission (FEC), which tracks campaign financing (includes a schedule of when candidates' reports are due, and a way to search through the ones already filed) and public funding of presidential candidates.
Another one to explore is OpenCongress. Includes a blog on current issues. Also lists votes, issues, and the money trail. Interesting stuff.
GovTrack.us has information on elected officials and bills before Congress.
Watchdog.net Looks to be a good site with biological info, earmarks, voting analysis, bills, contributors, and even tracks how votes line up with contributions, by date. It appears to be out of date but if the info is fresh, it will be a great research tool.
Politicks offers up a site comparing all potential 2012 Republican presidential candidates. This site keeps popping up on searches for info on Republican presidential candidates. However, I am a little leery of it because I can't see who sponsors it, so I don't now their motivation. I'll keep looking, but I'd like your feedback on this if you can find anything.