MS Chart control can be used in .NET 3.5 also.
Microsoft Chart Controls for Microsoft .NET Framework 3.5[
^]
Before this chart control you had to use a 3rd party component like
ComponentOne,
Telerik,
DevExpress etc.
You can build charts manually using either javascript, flash, imaging etc, but I don't see the point reinventing the wheel. It's a lot of good components out there and the MS chart control will covor most basic needs :)