I use DivX official, XviD official, Quicktime alternative, Real Alternative and CoreAVC. 5 separate installers might seem long winded, but this way I don't get issues. I routinely find codec packs unreliable.
The only codec(pack) I recommend is ffdshow. Its more efficent for Divx/Xvid but COREAVC gets my use for AVC use.
I usually end up installing xvid for encoding purposes, but not for decoding. Just never had any luck configuring xvid encoding in ffdshow.