One of the most useful resources for researching American Politics is the Congressional Quarterly Electronic Library. The library is actually made up of 8 distinct databases and includes primary and secondary information on American politics in all its various facets.
Of particular interest are:
The CQ Researcher focuses on a specific issue each week and provides a comprehensive background on the issue--legislative activity, historical background, current developments, and a bibliography for future research. Online version is searchable and goes back to 1991. CQ Weekly focuses more specifically on congressional activities and developments.
CQ Congress Collection
CQ Congress Collection is a dynamic, data-rich research and reference tool allowing a sweeping historical analysis of members of Congress, their legislative voting behavior, interest groups, and their interactions in crafting public policy.