Here. Duncan [1] points out Tim Dawson's set of WinForms controls, all of which are either free or cheap for commercial apps. Not only are the controls well-designed and flexible, they're also documented with a set of tutorials and provide an extensive design-time experience. I don't know how someone can make a living giving this stuff away, but that doesn't mean we can't enjoy Tim's generosity.
[1] http://weblogs.asp.net/duncanma/posts/40415.aspx
