Whether we're discussing Windows or OS X machines, the standard media player that ships with the computer is, for lack of a better term, sub par. Both Windows Media Player (Windows) and Quicktime (Mac) have very limited choices when it comes to file formats that they will play back. Because of this, many have turned to third party media players such as VLC, which has support for nearly every type of media file used.
However, some still prefer the more polished interface that both Windows Media Player and Quicktime provide. If this is you, then you are not completely out of luck. Try some of these useful download to improve your basic media player's functionality.
Windows Media Player
Out of the box, Windows Media Player supports a wide variety of file formats. Despite this fact, some of the most popular formats are still not natively supported. Whatever the reason is for Microsoft not supporting more file types, the developer community has stepped up and released codec plug-ins that allow for a larger variety of play back. This popular codec pack adds support for nearly any movie and music file that you might come across. So whether you rip your media to your computer, or purchase and download through a website, you will now be able to use the all too familiar Windows Media Player for all of your playback needs.
Quicktime for Mac
Much like Windows Media Player, Quicktime for Mac lacks support for many popular file formats. Not surprisingly one of the popular file types missing include the standard Windows formats. Much like with the codec pack above, Perian is an open source plug-in that adds a plethora of file formats to Quicktime's arsenal. Another great feature of Perian is the added support for a variety of subtitle formats, which as any foreign film lover will tell you, is a must. If quicktime is your thing, then be sure to check out Perian, the self proclaimed "Swiss Army Knife for Quicktime."