I think that there's a lot to argue on the merits and downsides of porn and masterbation. Either way, this thread was created in order to find ways to break the addiction. Let me offer some methods that may or may not work, but are probably worth trying.
First, amass reasons as to why you want to stop your behavior. Research how the effects of masterbation may be bad for you, or at least not in your best interest. Maybe draw on some personal experiences or beliefs. Imagine what it would be like to be free of this controlling addiction and to regain/create conscious control for yourself. Write down your reasons and reconnect with them everytime you even think of porn (there are detailed methods of connecting two thought patterns, such as the one
right one this website). Make specific guidelines for what you do and don't want. You could even make a promise to a trusted friend. This is your purpose, this is what can provide motivation whenever you need it.
Next, use the idea of applying overwhelming force (we all know of this, right? Well,
just in case). Maybe you could generally spend less time at the computer or spend your time at the computer more efficiently? Maybe you could visit a website promoting non-sexual nudity like someone else suggested? If you're really commited, dump all your porn right away and never look back. Do all that you can to prevent yourself the opportunity to masterbate. Mingle with people more, go to bed earlier, and most importantly, don't think about it!
As they say, resistance is futile (but redirection is more powerful). Mentally, connect porn to disappointment instead of pleasure in any way you can so your body isn't attracted to the feeling. Try developing the habit of doing a certain ritual before you allow yourself to masterbate. Maybe run around your house, briefly connect with someone and review your purpose you created? You could even make this a chance to be productive in another area, like forcing yourself to play the piano before you masterbate. If you are into playing music, you'll probably end up distracted, which is the goal here; giving your focus to something besides porn. At the end of the day, be sure to congradulate yourself if you've made it through successfully. Be proud that you're changing your life for the best! If you fail, pick yourself up and use that failure as more motivation to keep trying until you win. If porn enters your mind, get excited about the opportunity to overcome it and improve yourself!
While everything is potentially going your way, be sure to create some type of habit to quell that need that masterbation once provided. Redirect the energy, as they say. Sexual energy can probably be expressed in physical energy, so be sure to have a opportunities to run and exercise yourself. If you previously had time for porn, you should have time for this (replacement).
I really don't know you and I don't know what will work for you; you need to decide and make plans yourself. As you read this, why not start now? Right now, commit yourself to making plans to overcome the addiction of porn and follow through with them! If you take all the steps you can to reach your goal and still don't achieve it, come back here and tell me I'm full of crap. I've spent some amount of time on this post trying to offer my help so I'd really appreciate it if you took this advice to heart and tried it. You owe it to yourself and partly to me. Immediate success or failure, try using this thread to keep track of your progress. We're all rooting for you here, whatever your goal may be!