Google Trends is a nice tool that gives you statistics about the terms used in Google web searches, in the form of curves. For instance, you can compare the curves of iPod, iPhone and iPad:
But there's also another interesting part, on the right: it gives you links to articles that were published at the moment when a peak occurred. The moments are correctly chosen for buzzwords like in this example, not always as well chosen for less marketing-oriented products. Anyway, that's often a way to apprehend the history of a technology, idea or movement.
Have a look at these curves: