Need a list of audio and video codecs.

I downloaded a lot of codecs from Yahoo, but some of my video files still aren't working. They say they need some kind of audio codec to play, but they don't specify which one.

Got a list of codecs I can download and try out? I do have the AC3 audio filter, Xvid, Divx, WMP 7,8,9 , Real, Quicktime, Macromedia Flash and Shockwave, and many others already.

I wonder if it might be in Windows Media Encoder. I'll try downloading that.