There are several prominent series of publications from the U.S. Congress, including those from committees and from subsidiary sites. This list of Types of Legislative Documents, created by the Law Librarians of Washington, D.C., might help to clarify.
A few commercial publishers have digitized large quantities of Congressional publications. Searching and access often are easier than with free sources, but access is available only to current members of the W&L community.
This is almost certainly the most comprehensive database of Congressional publications, some dating back as far as the late 1700's. Includes the complete texts of hearings and most other documents. An interesting sub-set of the database provides legislative histories. (Law Library subscription.)
These collections of Congressional documents are provided without-charge for all users by the Federal Government.
Online coverage generally begins with the early- to mid-1990's.
Official and free.