By Joe Armstrong; Pragmatic Bookshelf, 2007, ISBN 9781934356005. Shows how to write programs that are concurrent, run on even hundreds of local and remote processors, and highly reliable, even during network and hardware failures.
Chad Fowler; Pragmatic Bookshelf, 2006, ISBN 0977616606. Shows how experts have already solved many problems, from latest Ajax effects to development time-saving automation tips.
By Dave Thomas, David Heinemeier Hansson, Leon Breedt, Mike Clark, James Duncan Davidson, Justin Gehtland, Andreas Schwarz; The Pragmatic Bookshelf, 2006, ISBN 9780977616633. First definitive guide to developing with Rails; Jolt-award winner.