BuildInternet has done some research with the help of Google and WhatTheFont, in order to create a list of Fonts Used In Logos of Popular Websites, e.g. Twitter, Digg, Vimeo, Tuts+ Network, Last.fm, Technorati , Flickr, Youtube and etc… You might find this article useful when creating the logo for your own website as well.

Source: Fonts Used In Logos of Popular Websites