Targeting elected officials and segmenting email audiences based on past actions(i.e. votes) isn't nearly as useful as being able to target based on upcoming votes. As such, bill cosponsorship status is a vital measure of the progress of legislation in Congress.
So, using publicly available information (Sunlight Labs, Congress.gov, etc), set up Vote Center to identify PENDING legislation that has been introduced but is sitting in committee and track current cosponsorship of that legislation.