Great new book on ASP.NET WebParts
I just finished reading the book "The Web Part Infrastructure Uncovered" by Teun Duynstee (a colleague of mine) and I think it's the best book available on ASP.NET WebParts. It's well written and contains a lot of interesting code examples. And: it's not expensive (less than $18 at Lulu.com).
If you're programming ASP.NET WebParts and you're curious about how to extend the WebPart framework, this is definitely a book to buy. Custom menu's, custom zones, custom security, custom catalog/editor zones, custom property-editors: it's all explained in this book with great examples. Also, Teun explains in detail how the webpart's data is really stored in the database, and how you can create instances of it without the need of a HttpContext. Only thing missing in this book is the integration with ASP.NET Ajax, but there are a lot of good books on Ajax already.
Details on the book here: The Web Part Infrastructure Uncovered.