I was changing some preferences in iMovie '09 when I noticed there's a cool font in the last tab - Coolvetica.
I was sure I don't have it installed on my system, so I dug in the application itself and there it was, together with some other nice fonts, like Duality or Strenuous, which I might use later for some titling in FCP - that's what those fonts were used for.
Right-or control-click the iMovie icon in Applications folder, and select Show Package Contents. Then go to Contents/Resources/Fonts, and double-click and install those you like.
I searched Hints but only found a story about one font in Aperture. People in the comments there are discussing the legality of extracting fonts from Trial software, but iMovie is on every new Mac.
[crarko adds: If you have iLife '09, I would think your conscience should be clear in using these fonts in other programs.]
Mac OS X Hints