Hey Penguinsfan, when I useta hit the bags good and hard one of the principles I applied was to stop the bag swinging by hittin' it. This helps break up a predictable rytHydromax that your opponent may take advantage of and also (ya gotta be careful, start with low amplitude swings and work up) helps develop incredible wrist strength and impact resistance.
If ya don't have a workout partner but you do have some time and money go get yourself a "double-ended-ball" . It's kinda like a speedbag except it's a solid ball suspended between two bungee cords. This first few hours on this will have just about anybody feeling like some uncoordinated-ass bumble-fuck, but it's fantastic for rytHydromax, timing, hand-eye training as well as a damn good aerobic workout. And if you really wan't to punish yourself get a dual double ender; that's two balls, hung and separated by a bungee. Use your hands and feet, high or low, and pretty soon you feel like yer dribblin' footballs during an earthquake.