With FFmpeg 0.5 there is a plethora of new audio/video file decoders and encoders, a new meta-data API, cleaner code, ffserver fixes, new muxers / demuxers, and various other features. Among the new decoders are for RealVideo RV30/40, MLP/TrueHD, Flash Screen Video, Monkey's Audio, and many other formats. There is also NVIDIA VDPAU support in FFmpeg.
The announcement of FFmpeg 0.5 can be found at FFmpeg.org along with download links. The complete change-log can be found via their SVN viewer.