1. VLC Player
VLC Player comes at #1 on my list. It is simply the best media player out there. It has plenty of features such as video streaming over network and it support multiple languages and plays almost anything you throw at it. I use it as my default player on Windows and my secondary player on Linux.
Pros: Plays almost everything you throw at it, multiple language support, has plenty of features
Cons: Confusing menus can be daunting to new users
Totem is a media player only found on the Linux platform. Like VLC, it supports many different file types (but not as much as VLC does) and is stock player on most Linux distros. It also supports DVD playback (which is a nice feature).
Pros: Comes with most Linux distros so you can instantly watch videos
Cons: It doesn't play some specific MKV files and does require additional download if codecs are missing
3. Media Player Classic - Home Cinema
Media Player Classic - Home Cinema is also another great alternative for VLC. It plays most media files you throw at it and it is light on system resources.
Pros: Plays most files and is lightweight on system resources
Cons: Interface isn't that appealing
4. GNOME MPlayerGNOME MPlayer is another video player that is only available on Linux platforms. It pretty much plays most file types and is quite similar to Totem player. Whatever Totem can't play, MPlayer should do the trick. It goes well with your existing video player as a backup.
Pros: Plays plenty of videos files perfectly, lots of customization options
Cons: Unappealing interface, requires some Linux knowledge to use
5. Windows Media Player
I know there are plenty of other players out there which I haven't mentioned (such as SMPlayer, GOM Player...) and I know they are pretty good. However, I must give #5 to WMP. Why? Well Windows Media Player comes with all Windows installation so it is right there when you need it. It plays all of the common media types and has a nice, clean interface. Most users will not need to look for another different media player and if they do, VLC is still the best alternative available.