flot

Recently I've been working with a Javascript library called flot, which does graphs purely in Javascript. It's a pretty handy tool for plotting graphs without resorting to Flash or Java - it's pure Javascript. Not only that, but it is really snappy and looks good! There's a cool example here that shows both the graphing capabilities and interactivity.

It's not as powerful as Flex by any stretch, but unless you need fancy morphing of graphs or things like that flot is just fine for you. And you have the benefit of not having to use Flex/Flash to do it!