The Congress is served by its library. Known around the world for its massive collection - it has 138,313,427 items in the collections (which include not just books but manuscripts and audio recordings) - it was established in 1800 as a reference collection for the legislative branch containing "such books as may be necessary for the use of Congress". The original collection was destroyed by the British when they burned the Capitol in 1814.
Thomas Jefferson offered his own collection of books for the reestablishment of the Library. Today the main building is named after him. At its centre is the reading room - which is magnificant. I had the privilege this week of going into the room whilst researching for a paper which I have been writing (and which is the reason Washminster has failed to appear for a couple of days - as I worked against the deadline for submission!). If you are in Washington the building is a must see.
The Library of Congress also contains the Congressional Research Service. I have the very highest regard for the quality and volume of material produced by CRS. There has been a long running debate in Congress about whether major publications should be available to the public - as they are from the House of Commons Library. The issue remains unresolved. However a website has been set up by campaigners, and many reports are available there. I find it an invaluable resource. The address is http://www.opencrs.com/