Media Preview - Fed up with Windows Explorer not always showing thumbnails for all of your media files?
K-Lite Codec Pack - K-Lite Codec Pack is a collection of codecs, DirectShow filters and tools.
CCCP: Combined Community Codec Pack - The CCCP: Combined Community Codec Pack is a codec pack specifically built for playing videos (including mkv).
Kawaii Codec Pack - Tired of bad media playback? I bring to you the ultimate solution: KCP
AC3Filter - AC3Filter is a high quality free audio decoder and processor filter.
VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.