Apress is planning a follow-up of their Microsoft SharePoint: Building Office 2003 Solutions book. It's title is certainly promising: Advanced SharePoint Services Solutions. I am curious about the content there will be in the book. This is the only info I could find:
Hillier also covers advanced integration techniques with related products like BizTalk Server 2004 and Content Server. Intended for you advanced developers who already know all of the basic SharePoint Services, this book will steer you to solve ultra-specific, advanced problems.
While browsing the site of the author, Scott Hillier, I noticed also that there is another workflow product for WSS I have not heard of. It is called the FlowBuilder and WorkFlow Engine and they describe it as:
The FlowBuilder WorkFlow Engine is a complete engine for supporting workflow initiated by SharePoint Document Libraries. You can capture events, send e-mail, assign tasks, and manipulate documents to automate business processes.
Pricing and details can only be received by sending an email to Scott. (I agree with Mike though that people should have this type of information directly available on their sites...). Anybody using this tool?