MPlayer
MPlayer is a free and open source media player for countless formats. These include PEG/VOB, AVI, Ogg/OGM, VIVO, Windows Media Video, Windows Media Audio, QT/MOV/MP4, RealMedia, Matroska, NUT, NuppelVideo, FLI, YUV4MPEG, FILM, RoQ, PVA, VideoCD, SVCD, DVD, 3ivx and DivX.