Cross Browser CSS Inspector --> XRAY
I may be a little late to the game on this one, but I just came across XRAY. XRAY is a bookmarklet that lets you inspect all of the CSS properties associated with any element in the web page you’re currently viewing. Best of all, it works in all of the browsers I use for testing plus some (Internet Explorer 6+, and Webkit and Mozilla based browsers - including Safari, Firefox, Camino or Mozilla). I’m still going to use Firebug and the IE Developer Toolbar for digging deep into a page and tweaking properties to get things just right, but having a common user interface across browsers for simple CSS inspection is great.