This Google project pulls data from a corpus of scanned books. Users can input words or phrases and Google will graph the frequency with with those words or phrases have been used in print over time. There are also advanced features that allow users to modify their searches with inflections or parts of speech.
For anyone interested in language or history, the Ngram Viewer offers the potential for leisurely fun or for more serious, scholarly research. As an English language teacher, this website seems like a good tool for understanding more about how language is used over time and for explaining to students the different contexts in which English words and phrases are used.
Usage of 'tackle' as a Noun or Verb between 1800 and 2000
Usage of 'read' with different Determiners between 1800 and 2000
The graphs above could be used in a language instruction context to demonstrate patterns of language frequency and usage. More information and sample graphs can be found on the Ngram About page. Happy Searching!