I spent several weeks this summer writing an ASP.NET 2.0 provider toolkit under contract for Microsoft. The centerpiece of the toolkit is a 120-page whitepaper documenting the provider model and offering lots of samples. It's now online (in 10 parts) on MSDN at the following locations:

In a couple of weeks, I begin writing phase 2 of the whitepaper, in which I'll document--source code and all--most of the built-in providers that ship with ASP.NET 2.0.