Possible choices:
Divx, version 5 just released
OpenDivx
The one true open and free video codec I know of and that is not 'idle', the Vorbis video project, isn't even in production. But at least we have a open and free audio codec which is |-| <-- so close to final release and already verry good (AFAIK only surpassed by MPC on high bitrates), Ogg Vorbis.
I'd say currently Divx is the codec of choice.
BTW, I know how to convert WMV's to RAW avi's and from there to what I like; but not how to do that with Real. Does anyone know a way to do that that dosn't include screenshots or a TV-Out?