Could someone please start listing off as complete list of codec's and (urls if possible) so I can make sure I have "nearly everything" installed?

I'll start off.

Divx 5.11 Pro
XVID 5.11
Nimo's Codec Pack 5 beta 9
Ogg (some .ogg codec)

What else is there that is like a "must have" for video and audio file playing? ( I ask since nearly all codecs I've ever heard of are free, it doesn't hurt to have them all).

Thanks in advance~!

DivX 3.11 - Decoder/Encoder (illegal hack)
ffdshow 2005-01-22 - DivX 4.X, 5.X, 3IVX, XviD, MPEG-2 (Decoding)
AC3Filter 1.01a RC5 - AC3 Audio Decoding
Nic's XviD CVS build (14/12/04) - XivD encoding and ffdshow WFV backend
OggDS 0.995 - OGG Vorbis decoding and OGM-support
VSFilter 2.33 - Subtitle support
Haali's Matroska Splitter 2005-01-29 - Matroska container support (MKV)
Morgan Stream Switcher 0.99 - Audio switcher for Matroska container
CoreAAC 1.1.0.642 - AAC audio decoder

I'd stay away from DivX 5.X, it's doesn't provides good quality, tends to "take over" other video formats during decoding and includes spyware. ffdshow works flawlessy, it's free and contains a lot of nice features.
//Danne

I would stay away from any 'Codec Packs'. They tend to make more problems than solve