I picked up Web Parts and Custom Controls for ASP.NET 2.0 from Wrox at B&N
last week.  So far on a scale of 1 to 10 I would give it a solid 7.  I find
that it is a excellent resource to help me understand some of the more
complex things about Custom Controls.  Then I can jump to the web or at least
experiment intelligently from there.  Here is a link to the book on Amazon
http://www.amazon.com/gp/product/076457860X/ref=pd_kar_gw_1/002-9136472-2912001?
%5Fencoding=UTF8&v=glance&n=283155

Let me know if you find another book that you like.

Regards,
Eric Immerman
Solution Manager Development
Allin Interactive

http://www.amazon.com/gp/product/0735615829/102-1791399-0263345?v=glance&n=283155

Developing Microsoft ASP.NET Server Controls and Components
(Paperback)
by Nikhil/Datye, V. Kothari, Nikhil Kothari
Peter Kellner
http://peterkellner.net