Customers often ask "what are the best books for SharePoint programmers?" and while there are a few good lists (like AC's) none contain all my favourites so I'm starting fresh.
Essential Books for SharePoint Development
These are the standard books that make any shelf complete.
Inside Microsoft Windows SharePoint Services 3.0, by Ted Pattison and Dan Larson.This is the best book for any developer starting out with SharePoint, and one of the best references to have around even after you know what you're doing. Once this book helps you understand WSS, you'll have a sound foundation to either go deeper or go beyond outside WSS into MOSS.
Professional SharePoint 2007 Development, by John Holliday, John Alexander, Jeff Julian, Eli Robillard, Brendon Schwartz, Matt Ranlett, J. Dan Attis, Adam Buenz, and Tom Rizzo. I'm a contributing author so I am biased, but this is the best book on developing MOSS solutions. Topics include SharePoint architecture, building a developer machine, using enterprise search, BDC, records management, web content management (including custom field types, site columns, content types, and , online forms, workflow, and the report center. My full review is here including links to sample chapters, the source code and forums to ask the authors questions.
Professional SharePoint 2007 Web Content Management Development, by Andrew Connell. This is the best book for developers working with Publishing Sites. "WCM" describes the features that have to do with using MOSS for public web sites and intranets (internal web sites). It's also a really well-written book with great examples that every SharePoint developer can learn from. Topics include: site columns & content types, search, content deployment, and workflow.
Microsoft SharePoint 2007 Wrox Box. Now this is cool - all of the Wrox titles that are on my list in one box, plus Real World SharePoint (which may not be essential but it's still a really good book, below).
Code Complete (2nd Edition), by Steve McConnell. Not SharePoint specific, but probably the best book on development for any platform. If you want to be a better developer than you are and only read one book, this is the one.
Good Books for SharePoint Development
These have great moments, but for whatever reason are not essential.
Real World SharePoint, by many SharePoint MVPs. People say that Wrox books feel like they're written by too many authors. This one turns that into a positive by providing 15 article-like chapters by the people who know these topics better than anyone else in the world. Intro by Mike Walsh (guru of the SharePoint newsgroups), branding by Heather Solomon, BDC by Nick Swan (BDC Metaman anyone?), web part development by Jan Tielens (creator of the SmartPart), security by Adam Buenz, forms-based authentication by Stacy Draper, workflow using both .aspx pages and InfoPath forms, IRM, upgrading from 2003 to 2007, and workflow using both .aspx pages and InfoPath forms. If any of these topics are for you, chances are it's the best content on the topic you'll find.
Honourable Mentions, or books I haven't read but hear good things about.
I won't provide Amazon links because I haven't done my homework, but these are easy enough to locate.
Microsoft SharePoint: Building Office 2007 Solutions in C# 2005, Scot Hilier. Scot's a great writer but I intentionaly avoided this book when I heard he had a section on building a developer machine, because I didn't want to be tainted while writing mine. And I never got back to it, I really should.
Workflow in the 2007 Microsoft Office System, David Mann. I used to say it was the best book on SharePoint workflow, but there's another one now so I can't be sure anymore. David's sharp, and the topic is in-demand so this is worth a look if you're going deep.
To be continued (and actively updated). . .
Tell me about any other SharePoint development books I should know about, or send over a review copy (use the Contact link to request an address). I do work through these as deeply as possible before writing about them, so allow some time to absorb their greatness. If I really don't like something, I'm not likely to rip it publicly and any less-than-great contributions will still generate publicity and interest as a user group raffle prize. I do realize that this list is (today) biased to just a few publishers and those authored by SharePoint MVPs, but i do believe this speaks to the quality of the MVPs and the apparent ability of Wrox and MS Press to consistently bring us into projects. These pedestals are not forever, they are targets for the next wave to take aim at. Have at it!