I also believe in God but not in the devil. As an explanation for evil I am leaning between these options:
1, God has, much like I do when I play SimGames, given up and said "Fine, you want to f**k yourselves over all the way to destruction then go ahead and do it, I'm sick and tired of trying to keep you from being a bunch of idiots!"
2, the choice thing.
3, the divine plan thing. Actually, I don't think that sounds all great, but it bothers me that people who disagree always use the argument "how could anything good ever come from this poor kid being murdered!?" - humans are humans, God is God. Ever read the book Flatland? A being which lives in a 2D world is not going to be able to comprehend a sphere. Likewise, divinity is so beyond humanity that our way of thinking is not applicable. It's not the same ballpark, it's not even a friggin' ball sport in the first place, it's spaghetti straining.