There are a few books such as Developing ASP.NET Server Control and
Components, MSpress which is currently the best book about the subject
(although it is written for v1, it still applies)
Then there are a few articles:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/ASP
NETContDev.asp
Note behind that link, there are more than one article. There are many more,
if you check the left treeview navigation.

Signature
Teemu Keiski
ASP.NET MVP, AspInsider
Finland, EU
http://blogs.aspadvice.com/joteke
> Anybody seen any good documentation, paterns or best practices on how to
> design and develop custom ASP.Net server controls?
[quoted text clipped - 11 lines]
> and communicating client side state changes beyond just s simple value
> back to the server?