A huge compilation of Win32 codecs:

Video:
- Win32 VfW DLLs:
    Indeo Video 3.2 and 4.1, Microsoft MPEG-4 v1 & v2 beta, Microsoft
    MPEG-4 v3 (also known as DivX ;-)), Cinepak Video, ATI VCR-2, I263
- Win32 DirectShow filters, decompression-only support:
    Microsoft MPEG-4 v3 (this decoder is slower than VfW one, but
    offers wider range of picture control features), Windows Media
    Video 7, Indeo Video 5.0, Motion JPEG (using Morgan Multimedia
    shareware codec)
- Open-source plugins:
    Motion JPEG (using libjpeg, very slow)

Audio:
- Win32 ACM DLLs, decompression-only support:
    Windows Media Audio (also known as DivX ;-) Audio), MS ADPCM
    Intel Music Codec
- Open-source plugins, decompression-only support:
    PCM, AC3, IMA ADPCM, MPEG Layer-1,2,3 (compression into MP3 is
    also supported), MSN Audio, GSM 6.1 Audio
- Win32 DirectShow filters, untested decompression-only support:
    Voxware Metasound, ACELP.net