There is a great application that allows you to play various video formats such as wmv, avi, mpeg, flv, mov, and more.

Follow up:

VLC is the name of the program and it allows you to watch videos of just about any type. Have you ever got a video from a family member or friend and could not open it? VLC is free and has a clean design! Meaning no advertising or confusing things within it.

I used to use a program called Storm Codec which can be found at www.softpedia.com for free also. In other words, VLC is a program that knows how to run different types of videos ordinarialy would require a specific program to run it. An .mov file would require that you use Quicktime movie player, .wmv files are played on Windows Media Player, and .flv files are flash videos and not many players can play them. These video are the type of format that Youtube's videos are.

You can find the offical website of VLC and download it by clicking here.

With all the various video formats out there its nice to know that a program can play them all.Quicktime files, Windows Media Files, Flash Video Files, Real Media Player Files, and Mpeg (mpg) Video files can all be played on VLC.

Related questions:

How do I play an avi file?
Where can I find a free video player that plays avi/wmv/mov/mpg/ogg videos?
Is there a video player that can play all video file types?