If you love Pragmatic Programmers books, you've now got a couple strong ones that teach a variety of open source geospatial tools and concepts.

Scott Davis' '''GIS for Web Developers''' and Gary Sherman (of QGIS fame) has '''Desktop GIS: Mapping the Planet with Open Source Tools'''. It's always good to have more books that teach on the projects that I love, but it's doubly satisfying when the authors are both great guys. Each one has written in a enjoyable reading style and they both know what they are talking about. I highly recommend them.