+6  A: 

I faced the same question a couple years ago. The clear answer to which option, at the time, was Dundas Charts. And indeed, we did use Dundas Charts, with ease.

Since then, MS has acquired their chart codebase and included it in their 3.5 framework. You can easily use it with ASP.NET. Check out this blog post:

http://weblogs.asp.net/scottgu/archive/2008/11/24/new-asp-net-charting-control-lt-asp-chart-runat-quot-server-quot-gt.aspx

<asp:chart ...

Another third-party controls library I've used for charting is Devexpress. It took very little time to get a product up and rolling with Devexpress (maybe even less), but in the end, Dundas had more functionality for customization.

Chris
+1  A: 

These options:

ASP.NET Chart Control gallery

In addition, don't forget to check out the ASP.NET Chart control (linked to by Chris). I believe that MS bought out the control from Dundas.

Cerebrus
+3  A: 

ZedGraph

sipwiz
A: 

If you are ready for some Ajax, look at the way SO draws the reputation chart. The tool is a Jquery extension named flot.

Flot is a pure Javascript plotting library for jQuery. It produces graphical plots of arbitrary datasets on-the-fly client-side.

gimel
A: 

I have used http://www.fusioncharts.com/ in the past and have found them to be very good.

Abhishek
+1  A: 

The Google Chart API with a ASP.NET wrapper

Julien Chastang