We all believe in "S'char Ve'onesh" (divine reward and punishment). So here's a tip for staying strong and guarding your eyes. Sometimes we tell a child that if he does a Mitzvah he will get as much candy as he wants in the next world. This isn't a lie because the reward will be much greater than this, but the child can't relate to understanding the true pleasures of the world to come. When we struggle with looking at things we shouldn't, we are also acting like children. The only difference is that our desires have matured into different "candies". Sometimes it can help to talk to the Yetzer Hara in his own language so he will understand. Next time you see something that pulls you to stray after your eyes, tell yourself that as a reward for not looking, G-d will allow you to have this very woman that you desire in the next world. Now obviously, the reward in the next world will be much greater than this. Chaza"l say that one minute in Olam Haba is greater than all the pleasures of this world put together! But sometimes this idea is too abstract for the Yetzer Hara to hear, and that can make it hard to relate to. Instead, when you see a beautiful woman or a picture of one, tell your Yetzer Hara; "you know you won't get her anyway, you just crave to gaze at her beauty, so I'll make a deal with you. Turn away now, and as a reward for turning away just this once, you'll have her in the next world as much as you want!". This truly isn't a lie here either. You are only talking to the Yetzer Hara in his own language so he can relate to the incredible reward that you WILL receive in the next world...
Besides, in the Kabbalistic sources, the holy Shchina is sometimes nimshal (a parable to) a beautiful woman, and the zivug (intercourse) of the neshamos (souls) in the next world is a pleasure we can't even begin to imagine. Everything on this world is a branch of the "root" in the upper worlds. If sexual desire is the strongest of the pleasures of this world, then the spiritual counterpart of this desire (it's divine root) will also be the highest form of pleasure in the world to come. But only those who repent and stay pure in this world will merit these divine pleasures.