the Google Books corpus of American English, 155 billion words in size. limited to what you can do via the website at Brigham Young University. The easy thing to do is type in a word or phrase and see its frequency by decade, going back to the 1810s. The interface allows you to look for collocates (words that go with other words), view charts showing relative word frequency in the corpus by decade, handles parts of speech, and gives you various limits and display options. Other kinds of analysis that might be done with text corpora can’t be done through the interface.