Microsoft has provided a very nice charting package that is available on the WinForms and ASP.NET and is included (built into) .NET 4. It is also available for download with .NET 3.5. It is a VERY robust charting package that is extremely customizable. In fact, you can even modify the images before they are sent to the user (in the case of ASP.NET). I am sure there is something this package can’t do, but I have not ran into it yet.
It is actually quite easy to use, but it is best if you read through some examples. The best way to get started in my opinion is to follow the first link below. If you go through the tutorial you will be in good shape. Once you have done that, you may want to check the second link out for additional references. Next check the official docs when you need more info on specific properties, etc. The final link is really just a cool snippet of code to get you started in the right direction if you need to generate your own gradients for your charts; for example in a bar or column chart.