I absolutely love doing this with vanilla ice cream and various sodas. The classic is, of course, A&W root beer for floats. But orange soda, cream soda, Dr. pepper and even regular Cola flavours are all so yummy!
Where I came from, we actually put vanilla soft serve inside of Slurpees, Frosters, or other soda flavoured iced drink like a slush. We called them Screamers, because of how cold they were.