you have plenty, but these are my three favorites:
mplayer - http://www.mplayerhq.hu/
Liked by a lot of people, my favorite choice. Comes with and without GUI. (set --enable-gui while configuring if you want this). Also supports most codecs.
vlc - http://www.videolan.org/vlc/
This is can be very hard to install from source, but google it, and you'll find a good howto. This player has very many codecs, and is my second choise after mplayer.
xine - http://xine.sourceforge.net/
Very easy to install, this player even has support for dvd-menues.
Hope you like one of these, and good luck