Elfring Soft Fonts is one of the leaders in Shareware fonts.  Several freeware fonts are also available at the site.

4 Fonts has 4 new freeware fonts each month.

Ray Larabie's Freeware  typeface of the week.

alt.binary.fonts.  The news group dedicated to fonts.

Microsoft's has a whole set of pages dedicated to True Type Fonts..  There are several free fonts here (they are include with Internet Explorer and Windows 95).

The type quarry at Three Island Press has some great Shareware fonts.  We use some of their fonts for our headlines.

The Internet Type Foundry has a large collection of fonts.  Most of the fonts are retail.

Garage Fonts are only retail, but it is a really good source.

Dixie's Delights Fonts is another good source for retail fonts.  There catalog is available online in Adobe Acrobat format.

FontFace.  A new shareware or freeware font every day.

P22 Type Foundry.  Lots of high quality retail fonts.