The Government Publishing Office's online version of the U.S. Code, with versions back to 1994. Titles, chapters, or individual sections can be downloaded in PDF. (The 2012 PDFs have the same text as the print version required for Bluebook citations, but more recent editions incorporate material in the main volumes and supplements.)
Current and historical editions of the U.S. Code, in addition to earlier compilations of federal statutes. This is the source to use for cite-checking, because its PDFs mirror the printed volumes and supplements.
Provides legislative history information and access to a wide range of congressional documents, including published and unpublished hearings, CRS reports, committee reports, and committee prints. If you're researching legislative history for a particular law, try ProQuest Legislative Insight.