Google Trends

http://www.google.com/trends

I'm sure some of you already know about this, but I found out this last year.
This is one of Google's features that shows you the search trends on the keywords that you enter. Basically, you can enter anything and see the search volume index, the top 10 countries, cities, and languages that the search was made in by frequency. You can also compare the volume indexes of different searches (separate by commas). Google doesn't show too many numbers, instead they show a very simple graph with years on the x-axis. I also like how Google did the scaling (y-axis): scale basis is 1.0, which means that if you see a spike that went up to 6, that means that traffic is 6 times the average.
I think that the graph is good for its intended purpose, it's not overloaded with numbers and the tool allows you to compare many search trends at the same time.

Hint: try typing in Christmas -it shows a cyclical graph :)