And, of course, if you are a pc user, you use Windows Movie Maker, free with xp, much easier to use than imovie(honest!), and has everything an architect needs to do movies of his renderings.
If you are a professional renderer, you can use expensive and hard to learn eidting software, but for me Wmm works just fine.
Besides, it's not just the program, it's how you use it
I did a small workshop about this at ArchiCAD University in Nottingham last week, and judging by the reaction of ppl that attended it, architect dont know first thing about movie editing. And the guidelines are really quite simple.
Small movie clips (10 to 15 secs), simple and slow camera movements, carefull choice of background music, intensive use of still images (dont go flying around) and some sort of story to stich it all together.