Taxation & Economic Reform in America (Hein)
An historical archive containing millions of pages of legislative history materials including the Carlton Fox Collection of historical legislation from 1909-1950, and other legislative histories related to taxation, economic reform, and stimulus plans.
Joint Committee on Taxation Blue Books
At the end of each Congress, the Joint Committee Staff prepare explanations of the enacted tax legislation. For each provision, the document includes a description of present law, explanation of the new provision, and effective date. For many provisions, the reasons for change are also included. Because they are prepared after the fact, Blue Books aren't exactly legislative history.
Old Editions of Standard Federal Tax Reporter (Hein) - PDFs of the superseded, loose-leaf volumes (1917-1985).