umm..hmm
http://www.mplayerhq.hu/homepage/design7/news.html
mplayer has most codecs available (look in codecs page) The problem is, right now the windows version has no GUI to it yet. so my suggestion is that if you use it, make a desktop shortcut to mplayer.exe and drag and drop movie files to it.
edit: I just discovered
http://deje.uw.hu/ this project that looks like a ok front end project...their are a couple more floating around
codec page of mplayer for recent codecs
http://www4.mplayerhq.hu/homepage/design7/codecs.html