Google Web Toolkit Solutions: Cool and Useful Stuff is a 112 page e-book by David Geary. The Ajaxian has posted a mini review of this book:
Over all, the book doesn’t skimp on explanations and code samples and is written in a clear style. It doesn’t address unit testing with JUnit, but I suppose you can get that information elsewhere. For those of you who like to learn by doing, this is a decent tutorial (and worth the $10 price tag) that can tide you over until the bigger GWT tomes come out.