There are a ton of Javascript charting libraries out there. Here are a few that I have used or researched recently:
There are many more examples of really cool things you can do with data visualization at http://d3js.org/ as well.
In my experience you can hit limits with these libraries (highstock in particular) where your browser's performance is really badly hindered based on the number of points you want to show on a chart and the number of charts you want on a given page. In this instance I am specifically talking about line charts, but I assume the same is true of other types. Does anyone have experience with the performance of different javascript charting libraries with large data sets and large numbers of charts on a given page?
jqChart is optimized for handling a large set of data.