Speed Bags

The speed bag is a small bag mounted on a short spring that immediately snaps back after it is struck.  It is used to develop timing instead of power. Speed Bag Central cites the benefits of speed bag training as keener hand-eye coordination, improved rhythm and increased punching speed.

Double-End Bags

The double end ball punching bag is one of the best tools in the gym. They are
nearly the size of a basketball with tight coils, one going from the bag to the ceiling and the other going from the bag to the floor. They are excellent for distance, footwork, punching without leaning and hand eye coordination. Timing of combinations can be achieved together with developing speed, rhythm and reaction timing.