The official website of the US House of Representatives provides an abundance of useful information, including schedules and calendars for current legislation and a variety of historical resources.
It's not quite as good as the House website in terms of providing information on current events, but the Senate's official home on the internet is great for historical and artistic exhibits online.
Roll Call is a newspaper devoted entirely to reporting events on Capitol Hill. The paper's website offers great one-stop coverage of news from the legislative branch.
In a slightly goofy move, the Library of Congress decided to name its legislative information portal after Thomas Jefferson. (Why they went with all-caps, we have no idea.) Odd name aside, THOMAS is a powerful tool for learning about current and past legislation and congressional policies.