The Hollywood Studios Use Linux for their productions. Some of the most advanced and best Multimedia creation software exists only on Linux. Which is odd when you consider the MPAA stance on the encyrpted DVD player and Linux...
Anyhow Media Players for Linux;
Xine
http://xinehq.de/index.php/home . Xine is the back end Totem (Gnome), Kaffeine (KDE), Gxine (GTK- This is my preffered Linux Player), Xine-ui (xlib), aaxine (ascii art frontend), opie (Xine for xaruas and ipaq), flxine (fltk frontend) , and so forth and so forth.
Mplayer
http://www.mplayerhq.hu/homepage/design7/news.html Most people like MPlayer... I don't care for it though.
VideoLan
http://www.videolan.org/ Xmms
http://www.xmms.org/ winamp inspired media player (Xmms used to be the defualt player in fedora- As of Fedora 3 I think, it should be HelixPlayer)
Ogle
http://www.dtek.chalmers.se/groups/dvd/ DVD player for Linux
Helix Player
https://helixcommunity.org/ This is the REAL Player OSS comunity project. helix is the REAL Player for Linux without some of the closed formats from REAL. RedHat includes Helix where as Mandriva includes REAL Player for Linux. There is also the content producing tools (helix-producer) linked on that page.
Beep
http://www.sosdg.org/~larne/w/BMP_Homepage beep started out as a fork of xmms. They have sinced strted to rewrite the player form scratch.
quicktime-x11utils
http://packages.debian.org/unstable/utils/quicktime-x11utils These are for playing quicktime files
FOSS software for producing MultiMedia;
to begin with there is an entire Live CD distro devoted to this. It is called dyne : bolic
http://www.dynebolic.org/ some of the software I am going to post is also on this CD;
K-Toon
http://ktoon.toonka.com/ Toonka Films was concerned that not enough intrest in creating animated films in spanish speaking countris in paticular in South/Central America so they produced this nice animation package.
LiVES
http://lives.sourceforge.net/ Linux Video Editing System
FilmGimp/Cinepaint
http://cinepaint.movieeditor.com/ used for frame by frame video editing and retouching
JaShaka
http://www.jahshaka.org/ this is an HP funded project.
Kino
http://www.jahshaka.org/ Basic Video Editing - Simular to Windows Movie Maker
FreeJ
http://freej.dyne.org/ realtime video manipulation and editing.
and these are just the free ones.