Designers Treat: A Web-based Font Viewer

myFontbook makes it easy to browse, search, and discover fonts in your own font catalog. Many font viewers take a long time to render, but myFontbook leverages your browser's native font rendering to deliver your font catalog quickly.

The font viewer window provides an overview of all your installed fonts, rendered and sorted for you convenience. Once your fonts display, you can browse your collection using the gallery or list view. You can also rate and tag fonts to organize your collection (you'll need to register to perform that).

My only problem with the interface is that you can't go back and forth, but other than that it's super useful app, especially for designers.