Today, the Library of Congress unveiled the beta version of Congress.gov, which provides free access to congressional bills, enacted legislation, and member directories. This new site will eventually replace THOMAS, the Library's current legislative information portal. Read the announcements on the Library of Congress blog and the Law Library of Congress blog, In Custodia Legis.
Like THOMAS, Congress.gov features the text of current and past bills and legislation, dating back to 2001 (compared to THOMAS's 1990, though the developers will be adding all historical THOMAS content into the new site over the next two years). Congress.gov also includes some new features, like biographies of current as well as past members of Congress (dating back to 1947) and an expanded collection of tutorials on the legislative process.
The most noticeable changes, though, are the slick design (which is more compatible with mobile devices), improved search functionality, and the use of permanent, stable URLs (links to legislation search results in THOMAS expire after approximately 30 minutes, although a separate site called Tiny Thom.as will render them into permalinks). The Congress.gov About page highlights other changes and outlines plans for the continued development of the new site.
The Goodson Law Library research guide to Federal Legislative History will be updated to reflect the new site's availability. In the meantime, be sure to Ask a Librarian about this or any other options for researching congressional materials.