Looking for a boxing workout

I have never tried a boxing workout but I am looking to drop about 20 lbs without losing a ton of muscle mass( I weight about 200 but have a small tire around my stomach).

I'm wondering if anyone can give me a link or a website where there are good boxing workouts for beginners. I have never tried one before and really want to try something new.

Any help is appreciated. Thanks.

Heavy bag will wear asses out. 

Anything boxers do will absolutely rip you up.

As far as muscle mass.

I wouldn't worry about that as much as the spare tire.  Can always throw in a lifting session here and there.