Every Friday, there’s a Rave in Gadgetzan on WrA. It’s cross factional, and in the Auction House.
So as long as you haven’t pissed off the goblins at some point, all are welcome. And I mean all. If you can’t handle a panda or a worgen in a santa suit or plate thong, this might not be your gig. Remember, this is a rave.
The event is called Club Trix.
It starts at 8pm PST every Friday night, and runs till midnight. (but I’m here well after, and there’s still music and people dancing.) They ask that you show up well dressed (but well dressed means a lot of different things to a lot of different people), and leave your pets/demons/ghouls at the door. In trade, there might be people peddling booze, and there’s usually Horde and sometimes Alliance side bouncers.
But, to make the whole deal a bit more real, there’s a website complete with live DJs playing a variety of music, especially trance (who even take requests) and an IRC chat channel. It’s worth checking out, especially if you have someone in your roster of RP alts who’s a party animal.