GeeThree.com offers a free sampler of their Slick Transitions and Effects
You can get 20 fully functional plug-ins for free!
Universal Binary for Intel and PowerPC Macs
(Plug-ins do not work with iLife '08's rewritten version of iMovie 7)
Give Slick software a try for free.
Requires Mac OS X 10.3.9 or later, including Leopard 10.5