MPlayer

From the site: “MPlayer is a movie player which runs on many systems. It plays most MPEG/VOB, AVI, Ogg/OGM, VIVO, ASF/WMA/WMV, QT/MOV/MP4, RealMedia, Matroska, NUT, NupelVideo, FLI, YUV4MPEG, FILM RoQ, PVA files, supported by many native, XAnim, and Win32 DLL codecs. You can watch VideoCD, SVCD, DVD, 3ivx, DivX 3/4/5 and even WMV movies.”

I think that pretty much says it all about the MPlayer capabilities..
To have an actual experience just download the Beta GUI version from the site, unless you just want to be GEEKY and use the command line version!!

You can also get the various skins for the Player.