The K-Lite Codec Pack has a couple of major advantages compared to other codec packs: It it always very up-to-date with the latest versions of the codecs; It is very user-friendly and the installation is fully customizable, meaning that you can install only those components that you really want; It has been very well tested, so that the package doesn't contain any conflicting codecs; It is a very complete package, containing everything you need to play your movies; and has different packages.

Latest Changes:
Updated ffdshow to build 2005-08-03
Added On2 VP7 [version 7.0.8.0]
Added AC3filter 1.01aRC5 (in addition to the already included 0.70b)
Updated Vorbis DirectShow decoder (CoreVorbis) to version 1.1
Updated MP4 DirectShow splitter (made by Haali) to build 2005-08-02
Updated Matroska DirectShow splitter (made by Haali) to build 2005-08-02
Updated Ogg Vorbis DLLs to version 1.1.1
Added VSFilter 2.36 (in addition to the already included 2.33)
Updated GraphEdit to build 041201
Tweaked various default settings
Is now able to detect and uninstall even more codec packs
Minor changes

Download: K-Lite Codec Pack v2.51 Full

Full contains even more codecs. It also has encoding support for various formats. This package is for power users and people who do their own encodings.

Download: K-Lite Codec Pack Standard 2.51
Standard contains everything you need to play all the commonly used formats. This package should be enough for the average user.

Download: K-Lite Codec Pack Basic 2.51
Basic contains only the most essential things. It contains everything you need to be able to play the most popular and widespread formats. It is small enough to fit on a single floppy. Also great for including on your movie CDs.