A list of
CODECs sources can be found here (choose one of these sources): 1.
Free-Codecs.com, 2.
Nimo’s codec pack, 3.
CoDecs & codec identifiers, 4.
K-Litecode Codec Pack
Also consider getting a backup player like DivX or VLC which has in-built codecs:
http://www.videolan.org/vlc/ (choose nearest mirror site)