[emacs] How to set the font size in Emacs?

I've got the following in my .emacs:

(defun fontify-frame (frame)
  (set-frame-parameter frame 'font "Monospace-11"))

;; Fontify current frame
(fontify-frame nil)
;; Fontify any future frames
(push 'fontify-frame after-make-frame-functions) 

You can subsitute any font of your choosing for "Monospace-11". The set of available options is highly system-dependent. Using M-x set-default-font and looking at the tab-completions will give you some ideas. On my system, with Emacs 23 and anti-aliasing enabled, can choose system fonts by name, e.g., Monospace, Sans Serif, etc.