Center for Responsive Politics ****
Tracks money in politics (both parties), to see who's responsive to what. Comprehensive financial disclosure database, including Senate, which declined to put its disclosures on the Web.
Project Vote-Smart ****
Non-partisan. Tracks legislators' voting records, and how often they voted with or against each special interest. Collects 'report cards' from various special interest, on how well or how poorly each candidate complied with their wishes overall.