The video/audio player extension that I've been writing over the last couple of weeks is now live on test.wikipedia.org. You can see an example here:
http://test.wikipedia.org/wiki/Image:Test_Bungy.ogg
Documentation is here: http://www.mediawiki.org/wiki/Extension:OggHandler
I want to put this live on all Wikimedia wikis in the very near future.
-- Tim Starling