Here are some cool electric arc videos. The second in this first series is one of my favorites. When an actual arc forms, it's a column of plasma. Since plasma is (very) hot gas it generally rises which eventually breaks the column, i.e., the arc.
Arc Videos
This is what started me on the path of arc videos. Someone sent a video of these tesla coils playing the Super Mario theme music. This isn't the one I saw but these are the same coils, I think.
Super Mario Tesla Coils