Fot you IE users this is a great tool, I turn it off and on as I need it
Internet Explorer Developer Toolbar
-- Explore and modify the document object model (DOM) of a Web page.
-- Locate and select specific elements on a Web page through a variety of techniques.
-- Selectively disable Internet Explorer settings.
-- View HTML object class names, ID's, and details such as link paths, tab index values, and access keys.
-- Outline tables, table cells, images, or selected tags.
-- Validate HTML, CSS, WAI, and RSS Web feed links.
-- Display image dimensions, file sizes, path information, and alternate (ALT) text.
-- Immediately resize the browser window to a new resolution.
-- Selectively clear the browser cache and saved cookies. Choose from all objects or those associated with a given domain.
-- Choose direct links to W3C specification references, the Internet Explorer team weblog (blog), and other resources.
-- Display a fully featured design ruler to help accurately align and measure objects on your pages.
-- You can now selectively enable and disable CSS parsing.
-- The Misc menu contains a color picker.
-- Several link reports are available.
-- When you select an element in the DOM element tree list, the selected element scrolls into view if it is not already visible in the browser window.