Pretty much everything you do in boxing is plyometric. Throwing punches itself is plyometric activity. The heavy bog could be conisdered extremely intense plyometric activity. Jogging is plyometric. Skipping is plyometric. Having said that, you're probably looking for some drills you can do to increase your upper body explosiveness. Have a look at this:

http://www.athletes.com/fun/kelly7.htm

Keep in mind plyometric drills will only be useful for you if you have a good base of strength already in place. In other words, I wouldn't even worry about adding any plyo drills unless you can do a perfect one armed pushup and knock out a set of 15 wide grip pullups and can squat 1.5 x your bodyweight.