Senate.gov, House.gov and Congress.gov are three online resources that are useful for reviewing voting records. Roll call vote tallies are posted to these sites within an hour of the vote, and this database contains records dating back to the 101st Congress.
In addition to the tallies, Senate.gov and House.gov provide descriptions that link to Congress.gov, where the actual texts provide further elaboration. Another useful resource is GovTrack.us, which allows users to filter searches based on the Congress, the Senate as opposed to the House of Representatives, and the category. This database contains information on everything from passages and amendments to cloture and veto overrides.