Depends which platform you're talking about, mac or windows. Worthy ones to get are DivX http://www.divx.com & 3ivx for a start (google 3ivx.) Mpeg 2 helps but it does cost money. Having QT Pro unlocks a no. of codecs for encoding which are already installed on your system. Also go to QT's Prefs & MIME settings & make sure all plug-ins are ticked. You can also dwnld some xtra 3rd party ones for free if you press update QT & are using a mac.