[gilgad13]

Open Congress: http://www.opencongress.org/ seems like something pretty close to what you are describing. I think its just a layer on top of the thomas.loc.gov system someone else mentioned, but it also does tracking of who changes/supports what.

Judging from the number of comments, it isn't very heavily used.

[mpgoetz]

I like Open Congress. In about 2 minutes, I was able to find out more about the SOPA bill ( http://www.opencongress.org/bill/112-h3261/show). Fun fact: you can send a letter to your congressperson straight from the page!