As far as motivation to box? I don't really need any.

At first I had to motivate myself to exercise and keep fit any way I could. Sometime I would just not want to exercise with every single part of me. But I just forced myself to do it, like it or not, and you always feel great afterwards...
When I started boxing though it was just plain fun... And I have to actually motivate myself to stay away from it if I have other important things to do...

Basically their is just so much to boxing... Even if it's purely to keep fit you can still have a LOT more fun with it than other basic exercising. The fact that you have a bunch of skills and techniques there to continually better yourself at and try to perfect,, well that's what lifes about. You can never be perfect at it, but working to be the best you can at it is what it's all about. Boxing makes you fitter, tougher, smarter (i think), more confident, happier etc etc... There's the motivation right there... When I stop boxing (and this is going to sound lame), I feel like my life is missing something that is essential to it's growth.
Once you really understand it and start having fun with it and living the lifestyle a little, motivation to box comes very easy....
(getting up at 5:30 am on a freeeezing cold day for a 5 mile run on the other hand is a TOTALLLLY different story... Don't ask me how I motivate myself to do that because I have no idea.. Sometimes it just feels like idiotic routine,, if nothing else..)