What I would recomend...
K-lite mega codec pack with media player classic. It will play pretty much anything thrown its way. No reason to install the entire pack either, only what you need.
http://www.afterdawn.com/software/vi...codec_pack.cfm
VLC for anything that doesn't work in media player classic.
Realplayer installed for realmedia codecs.
Quicktime for its codecs.
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MediaInfo as a last resort in case I ever run into a file that I can't seem to play. It basically tells you what is inside your media so that you can google for what codecs you need to download. I have never needed it though.
http://mediainfo.sourceforge.net/en
:EDIT:
I will say one last thing though, the VLC icon is ugly. I always change it to something else. x3