Nonprofit dedicated to tracking federal legislation. Pulls in legislative information from government sources, such as GPO (103rd Congress/1993-present; selected historical data), as well as voting data, committee info., etc.
To find CRS reports, do a Google search for CRS and a policy issue, e.g. Google for: CRS immigration. These non-partisan reports are created by the Library of Congress' Congressional Research Service for members of Congress.
This guide, from Duke University, succinctly describes the steps a bill goes through in Congress to become law. Note, that some links are to Duke's subscription-access resources.
This list includes some free legislative histories of recent laws (see the bottom of the list). This list could be consulted to identify possible search topics for Govinfo.gov