Just want to chime in and say that I too am a married man dealing with this right now. I add my voice wholeheartedly to say:
1- He has to want to change. And even if he does, it can't come overnight. Addiction is by definition irrational. Behavior addictions (porn, masturbation, gambling, shopping, hoarding) operate by the same brain pathways as drug addictions. Even though you know you are destroying yourself and hate it, you feel powerless to change. There are very good neuro-biological reasons for this. It is truly a form of bondage.
2- A supportive spouse works wonders. Don't be distant, but express real love and intimacy. Porn is just an imitation of real intimacy but can never offer the real thing. Don't police, but ask him how you can help and how he wants you to be involved. It's true that addictions destroy relationships, but it is also relationships that destroy addictions. I have felt the struggle of having to confess a "slip-up" and seeing the tears. It is horrible and each time I wonder if I can do it again, but I have to if I want to regain trust.
3- This is really, really hard work. One way to be supportive is to do your own hard work too. Everyone has something they should be working on. We have been regular in our individual and couple scripture study and prayer. To get the help I need from the savior I need to do everything else in my life and the church that I can to be righteous. We are doing this together, and over the last 3 months we both feel like we are stronger spiritually than before, and we are definitely closer to one another as well.
4- He needs the atonement to carry him through, but you need it just as much too. Remember the twofold purpose: 1- forgiveness of sins and 2- carrying our burdens. Since you have no ability to directly affect another's choices, your best focus should be to spiritually strengthen yourself as much as possible. Not only is it a supportive example, but you will have much more powerful prayers to ask for help on your husband's behalf.
Although it is awful to have this in my life and in our marriage, it has also given me something that I know I can't do alone and forced me to rely completely and sincerely on the savior. I think it is doing the same for my wife. The Lord works in mysterious ways, but maybe finding a way through this is what we need to help us build the faith we need for salvation that we might otherwise not be sincere enough to seek out.
(p.s. A quick note about internet filters- They work well to help someone who is trying to avoid porn and needs it to be more difficult to get to. They won't help at all (and might hurt) if used as forceful barriers. The addicted brain will get what it wants one way or another. As far as to protect kids fom initial exposure, don't forget there are multiple different browsers, many file sharing programs, bit torrents, MSN, video chats, skype, smart phones, etc... pornography can come through any of them, so the simple web browser in my mind is obsolete except for the most inexperienced of computer users- which will not be your kids)
