Mac OS X now has a very basic, built-in font sampler, at least as of 10.7.3. If you don't care about having customized sample text, Font Book can do it without any add-ons.
Select the desired fonts in Font Book, choose Print from the File menu, and choose "Font Book" in the pull-down menu for printing options near the bottom of the dialog (the one that also says Layout, Paper Handling, etc.). If you don't see this menu, click on Show Details to display it.
You'll have the ability to choose from among three reports: Catalog (upper case, lower case and numbers, optionally grouped by font family and in a size of your choosing), Repertoire (a chart of every character that each font can print, also in a size of your choosing), and Waterfall (font details and the same basic sample in increasing font sizes of your choosing; seemingly one font style per page).
[kirkmc adds: I don't know when this was added, but this is quite nice. For most people, this will be more than enough. Note that this does not work with Mountain Lion; the Print command is dimmed when you select fonts.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120708022333618