FontXplorer
This program allows you to look at TrueType font files without having to install them or to double click on them individually. Just point the program to a folder with ttf files, and it will load them up in the left panel. Click any of them to test them out, you can even type your own text to see how it looks in that font! Now supports OTF files!
Download the source code.
Download the binary.
Updated Sep 11, 2012.
Previous versions:
Version 1: Source,
Binary.
This program and its source code is licensed under the BSD 2-Clause license.
Last updated sometime in September 2012.