I dipped my toe into the 1st (and last it seems) PragProg LOTY, learning a tiny bit of Haskell. I've still never studied functional programming much, but would like to.
This article at defmacro called ”Functional Programming For The Rest of Us” attempts to ease you into the mindset with some “here's what you'd code in Java to simulate FP” and I think it's rooty-tooty. (...or is rooty-tooty ‘bad’? The only reference in my head is from the original The Philadelphia Story movie, and the context is questionable).