

"Twitter meter let's you query an index of all the words that have been sent to Twitter's public timeline (since 11/6/2007) and plot the number of times that word was used over time".
You can search for one word, or many at once.
Each day is represented on the graph by a dot which displays the date and the number of times the word(s) you searched for was mentioned.
I find it to be a very interesting tool that can be used to compare brands/products/topics' popularity on Twitter (for example, Wikia VS Mahalo or Nike VS Adidas).
I wish there were an option to export the results as a high-res Jpeg or an excel sheet, for research/documentation purposes. Hopefully this feature will be available someday - Mr developer, can you please add it to your todo list? :)
Have a look at Twittermeter here.
Via @DrBaher