I have to put in a word for MacCaption. :) It is the best although not cheap. It has very advanced subtitling features, and of course closed captioning.
BTW the comparison chart on Zeitanker's page is very out of date for MacCaption. They used a version from 2006.
Please check out:
http://cpcweb.com/why_choose_cpc/
Thanks,
Jason Livingston
CPC Closed Captioning