I have 2 media players I use.
Media Player Classic (MPC)
Good
-simple interface, nothing flashy
-plays any kind of file, including .rm and .mov
-very low CPU usage
-several different rendering modes
-mousewheel volume control
Bad
-the controls are always attached to the video window (sucks for dual monitors)
BSPlayer
Good
-controls and video are always separate windows (great for dual monitors)
-it remembers that I want the controls on monitor 1 and the video in fullscreen on monitor 2
-lots of different rendering methods
-very low CPU usage
-can skip frames to keep the video and sound in sync
-supports vsync
-intelligently adds files to the playlist if they have the same file name except for the last few digits (gaysexCD2.avi is automatically added to playlist when you play gaysexCD1.avi)
-BSPlayer automatically opens to where it was when it was closed, such as gaysexCD1.avi at 10:31
Bad
-installs spyware which can easily be removed
-your gf finds out you're gay because it automatically opens gaysexCD1.avi at 10:31
For watching movies on a second monitor, I think BSPlayer is by far the best. Media Player Classic is all around good since it plays all file types. VLC is the last resort player because I hate the interface but it works on any file. My gf's Mac couldn't play any of my xvid movies through Quicktime, even with the codecs, but VLC worked right away.