Use Hein Online to find Congressional and Presidential documents (historical and current).
Hein includes a lot of different types of resources - once you have search results, try narrowing down to just Congressional or Presidential sources (to exclude the law journals and legal cases).
Use the Serial Set to search US Senate and House reports, documents, and journals from 1817-1994.This can be useful but also difficult to search - ask Simon for advice on selecting useful keywords and subjects.
Use this to search for bills, committee reports, and committee hearings. Most useful for 1980s-present, although at Swarthmore full transcripts of (published) hearings are available from 1824-present.