Beamer for Mac: AirPlay any movie from your Mac to Apple TV
Drag any movie file onto Beamer and it will start streaming wirelessly to your TV with Apple TV instantly. No jailbreak required.
Zach Poff: Software
A variety of homespun video presentation software for all your art installation needs.
HandBrake
"HandBrake is an open-source, GPL-licensed, multiplatform, multithreaded DVD to MPEG-4 converter, available for MacOS X, Linux and Windows."