Statutes at Large
U.S. Code (USC)
The information above comes from FDsys (GPO) site on Public and Private laws.
Public Laws can be found through these sites:
US Statutes at Large can be found through these sites:
Published legislative histories can be very helpful for tracking the history of legislation, especially if it took several Congresses to make it all the way through the process. A legislative history tracks the history of a law from its initial introduction all the way through its enactment by Congress. This includes the various versions along the way as well as the related debate, reports and testimony or hearings.
ProQuest Congressional [NPS ONLY] does a nice job of not only tracking but also linking to all the various pieces.