For those web developers out there using FireFox,you have to install the Firebug extension. It lets you explore the DoM in far more detail than ever before.
I can't tell you how much time this extension has saved me this year. Get it, install it and give it a whirl. You wont be disappointed I promise.
Microsoft have released their Developer Toolbar for Internet Explorer which goes some way to providing the same functionality for the Microsoft die hards out there but its a million miles away from our friends over at Mozilla.