Maybe like all of you guys already have this one, but since I didn't see it here I'd like to share it anyway. It's called 'Dust-Me selectors', and it's a nice little tool that browses through the CSS of the website you are currently viewing and returns which CSS parts are left unused. I often find myself tweaking around and debugging with CSS (which creates a lot of code mess) but I always kind of forget to 100% clean up the code afterwards. This tool helps me a lot to locate the obsolete parts.
A link is here:
http://www.sitepoint.com/dustmeselectors/
Oh and it's from Sitepoint by the way