I read somewhere that the best way to stimulate the prostate is through the anus, so I tried sticking a bunch of things up my ass. I wanted to find something innocuous that wouldn't be suspicious if I left it lying around. I finally came up with something. You know those plastic bottles of mini M and M's? There are two sizes (I prefer the longer one). Simply insert it into your ass (careful not to push it all the way in) and then jerk. It will heighten any experience, doesn't have to be even masturbation.
When I'm masturbating, I like to hold it in with my butt muscles until I'm about to orgasm, and as I'm orgasming, push it out of my butt, just like taking a crap. You know how it feels so good to take a crap when you have a big one? Well, this combines the sensation of an orgasm with the sensation of taking an awesome crap. It's heavenly.