Bookmarklet: XRAY

XRAY is a bookmarklet for Internet Explorer 6+, and Webkit and Mozilla based browsers (including Safari, Firefox, Camino or Mozilla). Use it to see the box model for any element on any web page.

XRAY works in Safari, Firefox and Internet Explorer. It helps you visualize the layout of your page. Add it to your bookmarks, and then on any web page, use it to see the position, margins, padding, dimensions and more details of any element.

XRAY uses lots of cool CSS3 features like border-radius, opacity, box and text shadow, as well as the HTML5 canvas.

Bookmarklet: Bookmarkme

Source: www.westciv.com