I have been enjoying 4clojure, although I found myself hitting a wall a few times, mostly due to not knowing about some function that I needed to solve the problem. It'd be great if there were hints available without looking at a completed solution - eg "try using 'reduce'".<p>Also, I have enjoyed the Clojure koans as well: <a href="https://github.com/functional-koans/clojure-koans" rel="nofollow">https://github.com/functional-koans/clojure-koans</a>