Well, MPEG rules. But they forgot to define a metafile.
Now there is video/vnd.mpegurl with the extension mgu,
like video/vnd.rn-realvideo aka ram or audio/x-mpegurl
and m3u for mp3s. More infos at
http://www.uni-bonn.de/~uzs106/Should be great for wireless imodetv etc..
Best,
H.