Three books related to MapServer and/or Open Source GIS are due to be published this summer. It's fascinating how a community with no paper books can suddenly produce a trio. Almost like how Hollywood can burp up a pair of asteroid/volcano/virus disaster movies simultaneously -- except that these books won't suck.
Tyler Mitchell's Web Mapping Illustrated (oreilly) was the first that I noticed. My understanding is that Tyler is covering everything from data processing and desktop GIS with OpenEV to web applications using MapServer. I proof-read his chapter on mapscript and found it very good. He's not re-publishing the tired old community scripts; these are fresh and clearly coded Python, Perl, PHP, and Ruby examples. I'm definitely getting this one. Should be available in time for OSG05.
Next, i was clued-in to Mapping Hacks (oreilly) by Schuyler Erle, Rich Gibson, and Jo Walsh. This book addresses not the mainstream analyst/developer, but hackers, inventors, artists, and hobbyists. Their interest in scripting MapServer seemed to grow with time and I'm very impressed with the sample code that I found on their companion site: http://mappinghacks.com. Has also been fun watching Schuyler latch onto Python. Or is it Python latching onto Schuyler? Being a fairly conventional GIS type, I think I have more to learn from this book than from Web Mapping Illustrated and am eager to pick it up. Should also be available in time for OSG05.
Lastly, there is Bill Kropla's MapServer: Open Source GIS Development (apress). I know very little about this book or its author, but do know the technical reviewer who assures me that it will be a comprehensive guide to MapServer installation, configuration, and templating. No publication date announced, but probably this summer post-OSG05.