In games, I always play the good guy. In Fallout, I was "Very good"; Mass Effect I was a paragon; and in Fable, I played the hero. I find it a little ironic since I always play a rogue-like guy too...but that's beyond the point. I always made the good choice, unless the end justified the means. It doesn't feel right being evil, or mass murdering innocents (minus the children in Skyrim, oh how I wish they could be killed).
In games, what's your alignment usually like? Feel free to share examples or stories too.