Enter the WhatFont tool created by Chengyin Liu. It’s a quick and easy way to find out what web font is in use. Roll over the type, and the font-family name pops up. Click on the type, and you’ll even get typesetting information (font-size, line-height, and color). This is particularly helpful when you find a site where the text is both beautiful and easy to read. Good web type isn’t just about using a good web font.
The bookmarklet claims to have full support on Firefox 3.6+, Chrome 9+, Safari 4+, Internet Explorer 9; and limited support on Internet Explorer 8.