Google Books Ngram Viewer
An online search engine that charts the frequencies of search strings within a massive corpus. If you search more than one expression (separated by commas), the chart will compare the frequency with which each expression appears in a corpus made up of books from the years 1500 to 2008. It can be used with a variety of languages (Chinese, English, French, German, Hebrew, Italian, Russian, and Spanish). The results can be used to find and select the terms or turns of phrase that are used most often.