Google Font Directory - *look* A directory of fonts for Cyrillic, Greek, Khmer, and Latin characters. All fonts in this directory are available for use on websites under an open source license and are served by Google servers. The Ubuntu font family is Included.
Liberation Fonts - Free replacement fonts for Arial/Helvetica, Courier, and Times Roman.
Open Font Library - The goal of this project is to collect free software fonts - those that may be used, changed and shared freely. It is a sister project to the Open Clip Art Library, and has released or hosted over 125 fonts. In mid-2010 this site was revamped and is in the process of migrating over all the existing fonts from the old site.