The Sunlight Foundation, a nonpartisan non-profit that seeks greater government transparency, has relaunched Capitol Words.
Capitol Words scrapes the Congressional Record, uses computer magic to organize the metadata, then presents an easy-to-use website where one can quickly search the favorite keywords of legislators, states or dates over the last 15 years.
This tool seems to have the most practical use for comedy writers and social scientists. I just ran a search for marijuana. Seems this capitol word appeared most often in September 1998 and by Republicans.
Interested in the judicial branch, then check out LegalLanguageExplorer.com (in beta). Search instances of phrases in Supreme Court opinions, and instantly download a list of cases. Marijuana appears in 127 decisions since 1800, and is most popular in 2001.