Word frequency lists and dictionary
from the Corpus of Contemporary American English

You can now freely download a list of the top 5000 words/lemmas from the 400 million word Corpus of Contemporary American English, which is the only large and balanced corpus of American English. Although there are many word and frequency lists of English on the web, we believe that this list is the most accurate one available (compare...).

The free list contains the lemma and part of speech for the top 5,000 words in American English. It is also possible to download other lists that contain the top 20-30 collocates (nearby words) for each of these words -- which provides useful information on word meaning and usage -- as well as to see which words are most common in certain genres (e.g. spoken or academic). It is also possible to download highly accurate lists for the top 10,000 and the top 60,000 words in English, with their top collocates as well.

If you want a printed version of the list with collocates, genre information, etc, you might consider the book Frequency Dictionary of American English: word sketches, collocates, and thematic lists (Routledge, 2010).