Macromedia Flash Player

Quicktime
Apple's Video Player

VLC
VLC media player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, ...) as well as DVDs, VCDs, and various streaming protocols.

I-Tunes

Music Match

Winamp

Audacity
Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems.

SUPER
A very efficient tool to convert (encode) or play any Multimedia file,without reading manuals or spending long hours training. It is a Multimedia Encoder and a Multimedia Player, easy-to-use with 1 simple click.

FormFactor - Another very good and FREE multifunction media converter. Very easy to use.

Online FLV Converter
Download online videos direct to PC / iPod / PSP. It's free!