Awesome list of resources! I'm currently working on a text-based Twilio app that simplifies updates on how their Senator/Representative votes on major legislation. Further down the line I'd like to tie in direct communication with Senators/Reps where they give a statement on why they voted the way they did, updates on when they're in their local offices, etc.
May I suggest you include committee votes where you can?
I've done a bunch of technology voters guides for Wired and CNET by crawling House/Senate records (what a pain) and that's one thing I always thought would be useful. Not enough attention is paid to them, and many bills don't get to the floor. There were plenty of SOPA committee votes on amendments, but the legislation never made it to the floor.
