You might also find eldoc-mode[1] and it's various mode-specific children (c-, perl-, ...) to a useful minor-mode. It displays a short string describing the function-at-point, and the order and name of it's arguments. Sort of zero-click docs. Whatever way it does it could probably be hacked up to display more complete docs in a split window or frame. Something I'll think about when I finally get an SSD :)

[1] http://emacswiki.org/emacs/ElDoc

Slime and Geiser give you this for Lisp dialects, including Clojure.