Google have recently released their Visualization API. I have spent some time looking into this API and implementing it into a project I am currently working on. For starters, this is a great, though relatively young API. There is a lot of choice as to how you can use it. I have been using the basic column chart to create some cool interactive charts. There is, so far, limited functionality and control over the the styles and user interface, but Google are bringing out regular updates and bug fixes.
It is definitely worth having a look at. Check out the video below which gives a more detailed outline of the product: