I'm quite certain that VLC is the best choice (supports a lot of formats) but if you're havings with that then
Maybe you would like to try GOM Player?
http://www.gomlab.com/eng/GMP_Introduction.html
It has the ability to play .Flv (Flash Video) files without installing additonal software.
M3U (Moving Picture Experts Group Audio Layer 3 Uniform Resource Locator, MP3 URL) is a computer file format that stores multimedia playlists. It was originally implemented in Winamp, although it is now supported by many applications.
An M3U file is a plain text file that contains the locations of one or more media files that the mediaplayer should play. Each location is placed on a new line. The locations can be either absolute or relative local pathnames (e.g., "C:\My Music\Heavysets.mp3" or "Heavysets.mp3") or they can be URLs. The file can also include comments, prefaced by the "#" character. In extended M3U, "#" also introduces extended M3U directives.
One common use of the M3U file format is creating a playlist file that contains a single entry pointing to a stream on the Internet. The created file provides easy access to that stream and can be used for things like downloading from a website or for emailing, or for Internet radio listening.
The file is saved with the "M3U" or "m3u" filename extension.