Well, in my many years of the masturbating, I have gone through many favorites. Lately I have enjoyed this one immensely.
I use a strap-on dildo (with the flat base). I get myself just wet enough to get it in without restriction then I put on a pair of tight pants, or a few pairs of underwear, something that will hold it in there. Then I just go on with my day, usually housecleaning, the more you move the more intense it gets. It takes awhile but is worth it. The hard part is not stoping and finishing the old fashioned way.
But the best part is you can't even tell you are doing anything. Maybe next week I will try it with the vibrator :-P