Any software that makes use of the FFmpeg libraries should be able to play ogg files without any trouble.
I run MythTV on one of my machines and it handles pretty much every format that I can play in wmp classic 6.4 or vlc on an XP box. (it's pretty much a dedicated DVR)
Otherwise I know the open source application "mplayer" works well for ogg (if you compile it on your own you need to make sure the ogg and vorbis libraries are installed before compiling)
Also VLC media player plays quite a few formats. It's available for Linux. I haven't used it to play an ogg in Linux, but I have played ogg files in BSD with it.