Since we consumers in the U.S. see these books on the shelf and recognize their publishers' branding, I will identify these by publisher. No slight to the authors intended! There is more method to this madness - I think that Wrox is on to something, and they actually have a useful, coherent layout of books.
Wrox - SharePoint 2007 and Office Development
This book turned out to be very good. They have a "tree" of related books, and this is at the top (the bottom being the "beginning" books). It explains a lot of stuff in fairly good detail. Best I've seen. It doesn't have a ton of code in it, but it has some, and it explains how things fit together.
Wrox - Beginning Sharepoint Administration
Beginning Sharepoint Administration was the best "basics" book I have seen. It had twice the detail in half the space of the "Administrator's Companion" book I have.
Apress - Workflow in the Microsoft Office 2007 System - It seems to go a long way towards explaining how things work, and it has some decent examples. Unfortunately it can't make the product function better than it is!
Microsoft - Office Sharepoint Server 2007 Administrators Companion - I can't say much nice about it. Maybe I dislike it because it was free. It never seems to have the answer to any questions.
Be sure to avoid older SharePoint books! There is little about WSS 2.0 or SPS2003 or anything earlier that would still be relevant.