Why try to stop??? Is it a problem? Masturbation is a normal healthy activity unless it is creating a problem in your life because you do it instead of doing other things when you need to.
I've never known anyone to try to stop successfully.
I have thought of this before too Scotty. My advice to you would be to reduce the amount of masterbation to about once a day or even less if you want. That way it will be much more meaningful and fulfilling.
I remember when I was younger(about 14 or so) I was embarassed about masturbation. And I tried to stop several times. I would think "ok, once I start HS, I am not going to masturbate anymore".
These were all very short lived endeavours. I think the longest I ever made it was about 3 days.
Now at 28 I have no delusions or wish to stop. I am not sure if you are young, but if you are I guarentee that it will be much more socially accpetable withing your peer group when you become an adult(assuming you belong to a western culture).
I saw a comic one time on the web that showed a couple of kids(two guys and a girl) hanging out and the girl says something like "I heard that 90% of all teenage boys masturbat, is that true?" And the two guys procede to object vehemently, and say that they would never do such a thing. The next panel shows the same guy as an adult walking out of the bathroom holding a girly mag and bragging about the masturbatory session he just had to his friends.
In truth it is very close to what happens in real life