Animationist is a clever and useful OS X app that lets you create animated titles, logos and images for use in iMovie, YouTube or Final Cut. It's currently available in the Mac App Store for a half-off introductory price of US$24.99.
The results look professional, and the default titles are so good you might not want to create you own designs, although you certainly can.
Animationist displays your edits in real time and animations can be done using keyframes, which should please video pros and semi-pros alike. Even light sources and font kerning can be animated. Of course you get borders, blur, shadows, color control, reflectivity and control of all the other parameters you would expect in an app like this (final effects must be rendered for full quality).