On a mailing list I am a member of, I just found mentioned this tool:

http://books.google.com/ngrams

It is available for a couple of languages and shows at which time the term searched for has been used how often.

It seems to have gone through the blogging world a few years before, but I had never heard about it, and found it quite interesting. Good for linguists as well as sociocultural research indeed. I tried (having written my thesis about human dignity and international law) “dignity”, and found the result rather unexpected at first.

Searching for “Google” shows, that results can be misleading without further analysis, though.