Mac OSX Must Have: Perian - Codecs for Quicktime
When I first got my MacBook Pro I was stoked. Everything was awesome, until I tried to watch/edit/do anything with video that I shot on my Casio Exlim digital camera. The camera shot video in a .AVI format, however it wasn't a 100% standard .AVI. I tore my hair out for hours. I cursed Macs. After a few days I had calmed down enough to starts the Internets... Then I found Perian, and I've never looked back.
Perian is a component for Quicktime that adds support for just about every video format other than WMV (just use VLC for that).
No Mac OSX install is complete without Perian. It's s life saver. If you haven't ever had the type of headache that I had or never want to: save yourself and get Perian ASAP!
Don't forget to donate a few dollars so that these guys keep up the awesome work.