I also use K-Lite Codec Pack ... well actually K-Lite Mega Codec Pack.

Please note the following:
1. Media Player Classic is included in the K-Lite Codec Pack.
2. K-Lite Mega Codec Pack also includes free Real Altenative and QuickTime Alternative that allow you to play Real Media/Real Video/Real Audio and QuickTime files.
3. It is very convenient to use a codec pack to play all audio/video formats. However if you use software like video editors such a codec pack can give you problems with codecs that are very difficult to resolve.