Great news! Microsoft has released a collection of free charting controls for both ASP.NET and Windows Forms! The only inconvenience is that they only work with .NET 3.5 (is it really an inconvenience? :-)), but they look great and offer the most commonly required functionality, at no cost.
Related links are:
Microsoft Chart Controls for Microsoft .NET Framework 3.5 download: http://www.microsoft.com/downloads/details.aspx?FamilyId=130F7986-BF49-4FE5-9CA8-910AE6EA442C&displaylang=en
Microsoft Chart Controls for .NET Framework Documentation download: http://www.microsoft.com/downloads/details.aspx?FamilyId=EE8F6F35-B087-4324-9DBA-6DD5E844FD9F&displaylang=en
Microsoft Chart Controls Add-on for Microsoft Visual Studio 2008 download: http://www.microsoft.com/downloads/details.aspx?FamilyId=1D69CE13-E1E5-4315-825C-F14D33A303E9&displaylang=en
Samples Environment for Microsoft Chart Controls download and documentation: http://code.msdn.microsoft.com/mschart
Windows Forms/ASP.NET Chart Control forum: http://social.msdn.microsoft.com/Forums/en-US/MSWinWebChart/threads/