I\'d be happy to have very soft character \">>\" instead of white-space, like this:
Mono develop http://primates.ximian.com/~miguel/pictures/Valabinding-classpad.png
EDIT: Just realized that blank-mode is superseded by whitespace. Load this and customize whitespace-style to at least contain tabs and tabs-mark. I currently have:
(setq whitespace-style '(trailing tabs newline tab-mark newline-mark))
There is also blank-mode which allows you to achive what you want and it gives you some nice functions to cleanup the whitespace to your likings: http://www.emacswiki.org/emacs/BlankMode