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I personally like "From Bash to Z Shell: Conquering the Command Line."

It focuses somewhat more on zsh (my shell of choice) than on bash, but one of the authors contributes heavily to zsh. Even so, bash users will see lots of great hints and tips. The shells' own man pages are more reference-style (see zshall), which I find heavy going when it comes to learning how to use the environment more effectively. The book explains use cases and provides examples in a way that makes the reference material more understandable.

Take a look at Unix Power Tools http://oreilly.com/catalog/9780596003302/.

I like the O'Reilly book, Learning the Bash Shell:

http://oreilly.com/catalog/9780596009656/

I keep it on hand as a reference for shell scripting, since it's both thorough and fairly portable.