Jammer(Six)

This is a slick little javascript bookmarklet that lists the attributes of various on-page elements:

Mouseover DOM Inspector

Just save it to your bookmarks toolbar (or wherever). When you want to use it, simply click on it and then mouseover the elements you’re curious about. When you’re done, simply hit escape.

This is a pretty nifty little too for quickly figuring out column widths, etc. when poking around on a site.