In general, my default installations add two different free plugins into Quicktime to handle files which Quicktime cannot handle by itself. Both of these plugins are very well implemented and tested, and both are rock solid in terms of stability.
- Telestream Flip4Mac Player – This application/plugin allows the user to view unencrypted Windows Media Files within Quicktime. This is especially important, as Microsoft no longer makes a Windows Media Player for Mac OS X. Unfortunately, Microsoft has not shared their DRM with Telestream, so any WMF file that is encrypted cannot be played on the Mac.
- Perian – Perian is a open-source application that installs as a System Preference, and extends Quicktime to read “everything else.” Basically, if it isn’t supported by Quicktime or Flip4Mac, Perian will.
I’m sure there are a few formats out there that this trifecta doesn’t support, but I haven’t found them (Encrypyed WMF excluded.) Furthermore, by having them installed by default, my users have to worry less whether a particular video will run or not, allowing them to be more flexible in how they perform their job.