I made a Clojure and FP themed wallpaper for myself

clojure-y-comb

There's few things as iconic as the Y-Combinator in functional programming. I must mention http://www.fatvat.co.uk/2009/04/understanding-y-combinator.html
as providing the actual snippet. To learn more, check out the wiki.

Update: http://imgur.com/Tgg54. Yep, it's 2880x1800.