Conduits PocketPlayer has recently release their player to support UPnP media servers.
Performance seems to be much better than Rudeo, and navigation through the media server is also quite smooth and easy. The playback of the mp3 is good, no lag, almost like you are playing from local drive. The only bug they have currently is chinese text (e.g. chinese artiste name or song name) are not displayed properly although it was okay if the same mp3 file are stored locally.
Makes WIFI indispensible despite all the 3G evolution ;)