I Googled
custom controls .net and got 542,000 hits. Several of them are Microsoft "white papers" that will likely hit exactly what you need (e.g., web controls, windows apps, etc.). It's really not very hard to do (my Visual Basic book shows how to do it for
VB.Net).
Dr. Purdum
Jack Purdum, Ph.D.
Author: Beginning C# 3.0: Introduction to Object Oriented Programming (and 14 other programming texts)