UPDATE: I find this script a bit intrusive. I mostly use the IE Developer Toolbar for tracking down the styles in the page-it works a lot like Firebug does in Firefox-highly recommend!
I got this script from a Sharepoint Solutions class-not sure if they wrote it… To help with your branding, you need to know what styles affect what. This script helps to reveal that.
Insert this script (attached as a pdf-wordpress freaked out when i published the code here) into a content editor webpart. It displays a div that shows what styles are being affected wherever you roll over with your mouse. Once you have the style information you need for the page, remove the webpart so that it is not published.