Batofar is THE place to see live electronic music in Paris. All of the best DJ's from Europe and beyond play at this club -- which is actually in a barge on the Seine.
The line to get in can be long on weekends, but on weeknights (it's just as happening with really good music) there should be no problem. You can also call and try to get on the list to avoid the lines altogether.
The music is mostly house or trance, but check Pariscope for who's playing. World-renown DJ's come to this little club -- it's the best way to see them. The crowd is attentive, really into the music, and NOT trying to hit on you like in most danceclubs.
The bartenders are friendly and the drinks are reasonable. As far as music - this is the best club in Paris.