When I chose a font for a project, I always spend way too much time. I'd like to type the copy in a program, and it would be displayed in each font installed on my computer so I can compare which font is the best (in terms of kerning, etc). This is a work-intensive alternative - I don't have time to do this, and my installed fonts change often.
I remember I used to be able to do that with free apps a long time ago under Mac OS 9 (Font Image Library, Font Gander, etc), and commercial font websites let you type custom text, but I cannot find any apps that do it for installed fonts under Mac OS X.