Been married for 1 year, and we've been together for 4. Have never had the urge to cheat on her. Once, another girl came on to me at a party though, and I used to have a crush on her. She came over and sat down in my lap and then tried to kiss me. I stopped her, and I'm proud of it.
One person asked "what if you where given permission?"
My answer to that is "I don't know". Sure, there are other attractive women out there, than I would pursue if I was single. But somehow, I would feel it was kind of wrong even if I had permission. When my ex broke up with me, I fooled around with some girl at a bar, and even that felt wrong (and my ex ironically cheated on me, and I knew. She ran of with the guy even, that's why we broke up)
We have even talked about threesomes, and I do find the thought trilling, yet I don't know if I could actually go through with it, even though my wife said it was ok. (Now you all might think I'm crazy).
But as someone has stated, if you are in a relationship and feel the urge to cheat, chances are high that your relationship is not that healthy. I have no need to cheat, since I have an amazing wife!