I suggest buying the books. They are excellent. If you have to pick two, I would suggest the O'Reilly book and the Joy of Clojure. The first is an excellent primer and the latter is really great at explaining the thinking behind the language. I also enjoyed Amit Rahore's Clojure in Action, as well as Programming Clojure by Stuart Halloway. I haven't read Practical Clojure.
The books are the best resources if you're trying to learn the language at a fast pace, but there is plenty of information to be found through Google as well. In the end the best way to learn is by doing.
The official cheatsheet is great for looking up how particular library functions work. Additionally, you can browse it to get an approximate idea of what the standard library offers. http://clojure.org/cheatsheet
4clojure offers many quiz-style questions designed to introduce various concepts of the language. http://www.4clojure.com/