http://www.myfonts.com/WhatTheFont/ - Just found this via Pixel2life. Upload a text-image (for example the hexus logo at the top of the website or even microsofts logo) and this tool will analyse the font in the image and comes up with a list of possible look a like fonts. Tested it a few times and it does work quite well despite my short experience with it. Its good if you see fonts you like in images but can never get the name of to search for them.
UPDATE :15th-Oct-2005
Found this while browseing, maybe of help to some 1
http://webxact.watchfire.com/
in the words of webxact this is what the site is/does:
WebXACT is a free online service that lets you test single pages of web content for quality, accessibility, and privacy issues.