The supersaw for trance (JP8000 I think), the hoover for gabber (alpha junos), the reese for dnb, squarewave bass for speed garage, MPCs for hip hop...

Most of all, though, I think dance music has been taken over by percussion. Maybe it's a result of the sequencer interface itself as a pervasive "electric guitar"...Cubase the new 303...maybe it most of all encourages drum programming, because drums lend themselves to being painted on a grid. I don't know.