highlight-indentation by AntonJohansson is a function made to show vertical guide lines of indentation levels (spaces only). The code is available at:
https://github.com/antonj/Highlight-Indentation-for-Emacs/
Appearance of guidelines is customizable by changing the face ‘highlight-indent-face’. By default, ‘highlight-indent-face’ inherits from ‘fringe’, which in most color-themes has an unobtrusive color.

This looks really neat. Is there a way to extend it to work with Lisp code? Something like the following:
(if n
| (let ((m 0) (p list))
| | (while (consp p)
| | | (setq m (1+ m)
| | | | p (cdr p)))
| | (if (<= n 0) p
| | | (if (< n m)
| | | | (nthcdr (- m n) list)
| | | | list)))
| (while (consp (cdr list))
| | (setq list (cdr list)))
| list)It would really improve the readability of long if forms like above (this is taken from the definition of ‘last’ in subr.el). – VegardOye
In its current form, the actual functionality of ‘highlight-indentation’ is very trivial: font-lock a space character followed by a fixed amount of space characters. So for it to work with lisp’s variable indentation some major changes are needed… – AntonJohansson
http://forum.ubuntu.org.cn/download/file.php?id=154714
https://github.com/ran9er/init.emacs/blob/master/20_aux-line.el