Preview Fonts quickly in Mac OS X
You can easily and quickly preview fonts within Mac OS X by navigating to the font directory in /Library/Fonts/ and changing the Finder view to Cover Flow mode. Now flicking through all your available fonts is easy as can be.
An alternative method to preview fonts is navigating to /Library/Fonts/ (Hit Command+Shift+G in the Mac Finder and type in the path) and then selecting list view, and then hit the Spacebar to enter into Quick Look mode, you’ll now be able to scroll through every font and see the full alphabet rendered in the selected font in lowercase and uppercase.

[...] discussed other approaches in the past that use Quick Look or Cover Flow view within the /Library/Fonts/ directory to see a complete alphabetical preview of any font face, but this is undeniably faster and easier [...]