Google Books Ngram Data
Google Books Ngram dataset is a corpus of about 5 million digitized books drawn from over 40 university libraries around the world by Google. Each page was scanned and the text digitized using OCR. The resulting corpus contains over 500 billion words in English (361 billion), French (45 billion), Spanish (45 billion), German (37 billion), Chinese (13 billion), Russian (35 billion) and Hebrew (2 billion). The oldest works were published in 1500s. The data is released in the form of n-grams (in light of copyright constraints). An n-gram is sequence of 1-grams, such as the phrases "stock market" (a 2-gram) and "the United States of America" (a 5-gram). More detailed description on the corpus can be found in Michel et. al. "Quantitative Analysis of Culture Using Millions of Digitized Books"
Corpus location: External Link