This one's for the pillow-humpers: get your pillow and put one end into a plastic shopping bag. Get naked, then grind the pillow with the bag over it. I like to rise a little on my hands and slowly move my hips in an up/down circle, so my penis only just gently rubs against the plastic. I've gotten great orgasms from this, it simply is amazing!
An added plus: when you orgasm, you can let fly without having to worry about cleaning it up!