This is totally sweet. Learned about this from a co-worker and had to share. Google used data obtained from 15 million scanned books to build Google Books Ngram Viewer. As most of you know, Google Books is a project to digitize as many tomes as possible. The viewer allows you to search for words and prints a graph showing how many times those words appear in the books it has digitized.
What's cool about this is that you're able to see trends over time. The datasets contain phrases of up to five words with counts of how often they occurred in each year. I searched for "zombie" between the years 1800 and 2000. I found the word mentioned in the early 1800s, increasingly found in books in the late 1920s and then spiking in usuage by 2000. Go ahead. Check it out and have fun.