Pew Research Center Politics & Policy often has reports, commentaries and polls on Congress and elections.
CQ Magazine is an important news magazine for covering events related to the federal government. It also has a "Floor Vote Search" on the left sidebar for searching how candidates voted if they were-- or are in Congress.
National Journal Reports on politics and policy.
Politico Commercial news site devoted to coverage of political news.
Washington Post Politics - coverage of results and campaign fundraising.
New York Times Politics has deep coverage and is also looked at closely by the campaigners themselves.
CNN Politics is like the New York Times in both the depth of coverage (much more video) and the recipricol influence it has on candidates.
HuffPost Politics liberal slant, but is useful for the latest political gossip.
FactCheck.org is a good place to find the latest rumors about candidates. This site describes itself as "nonpartisan, nonprofit "consumer advocate" for voters that aims to reduce the level of deception and confusion in U.S. politics."
PolitiFact A project of the St. Petersburg Times that tracks the claims and campaign promises and subsequent words and actions of politicians and pundits.