The overall chart is a great example of beauty and graphical simplicity. The letters correspond to a scrolling column of stories that tie in date-wise to the stock price. Drag the main chart around and the column of stories moves up or down to reflect the period now visible in the chart window. The bit at the top, meanwhile, is a longer timeline+chart which can be used to narrow or expand the larger chart below (by grabbing the two vertical little tweezer things, there’s probably a fancy name for them) and pulling together or apart.
There’s nothing revolutionary in here, but it’s executed very well, and to me is the first time that Google has really shown that it intends to eat into Yahoo!’s core market big time. There’s lots of other data on the page — all that one would need to make an investment decision, I’d wager — but the chart is the thing. What would be an afterthought elsewhere turns into a really dynamic tool. Exciting stuff.