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
Jack Purdum, Ph.D.
Author: Beginning C# 3.0: Introduction to Object Oriented Programming (and 14 other programming texts)