The Brush Tease:
Almost any soft brush will work. If you don't own one, you can pick up a soft paint brush (from 1 to 2 inches wide) at any paint or hardware store. Get the softest and narrowest one you can find. If you have the money, a large sable brush (available at your local art store) is an excellent choice, though they are often expensive.
What you want to do is gently stroke the underside of his cock with the brush. Use the lightest stroke you can, especially at the beginning of your session. You can use heavier strokes as the session progresses. Pay special attention to the very sensitive area just below the tip. Press hard enough to make his cock “jump” if you can. That means he can not only feel it, but you are really getting to him.
You can keep this type of cock teasing up for as long as you like and the odds are he will never reach a point where he will be able to cum. But it will drive him crazy. Don't be shy. You can tease his nipples and other erogenous zones if they are sensitive enough.