The Corpus of American English is the first large corpus of American
English, and it is freely available online. It contains more than 360
million words of text, including 20 million words each year from
1990-2007, and it is equally divided among spoken, fiction, popular
magazines, newspapers, and academic texts (more information). The
corpus will also be updated at least twice each year from this point
on, and will therefore serve as a unique record of linguistic changes
in American English.

The interface allows you to search for exact words or phrases,
wildcards, lemmas, part of speech, or any combinations of these. You
can search for surrounding words (collocates) within a ten-word window
(e.g. all nouns somewhere near chain, all adjectives near woman, or all
verbs near key).