One day I was lucky enough to discover that although a guy cannot actually have multiple orgasms the way women do, you can draw out their pleasure so that it feels like their orgasm is continuing long after they've finished actually cumming. My guy considers this to be his own kind of multiple orgasm and one hell of a great treat when I do it. Now, the reason I don't do it all the time (although I'm sure that he would be very happy) is mostly because I usually don't get off while I'm concentrating so much of my attention on his pleasure. So of course it's something special rather than every day. Also, despite the fact that we're both in our early twenties (as in 20 and 21) and he's at his sexual peak for all intents and purposes, it takes him awhile to recover enough to get it back up afterwards. Which means that chances are, no sex for at least half an hour (about twice the normal amount of time it usually takes him). Since I prefer orgasms during sex to any other kind... well, you get the picture.
However, when I'm wanting to feel in power and in control, and absolutely drive him wild it is something that I take particular joy out of doing.
It starts off with teasing. Mostly in the fact that I have him lie on his back and then I start to touch all over his body, finding his most sensitive spots with my lips and fingers. Two notes for this part: I do not let him touch me back and my touch on him is extremely gentle. In fact, I'm barely touching him at all. I run my fingers in little trails, and I actually never touch such erogenous such as his nipples, earlobe, or his penis. Instead I trail all around them, working little circles around his chest and slowly working inwards, as soon as I get to his areola I start moving away again. Now, most guys do not have the discipline not to move while you're doing this to them, but I find it's a lot more fun if you don't tie him up and he'll willing lie there while you tease him. The reward is definitely worth the torment that you'll be putting him through.
After spending awhile moving so lightly around his erogenous zones, I start to press a little more firmly and I'll let my fingers actually trail over his nipples, penis and balls - but I pay NO SPECIAL ATTENTION TO THEM. Just trail them over like you are the rest of his body parts and move on, don't stay there. Trust me, it will drive him absolutely mad.
Now you may have two questions at this point: 1. Why am I spending so much time prepping him when he's already hard as a rock? and 2. What do I do when he keeps trying to grab me and throw me down?
Well the answer to #2 is to be very firm, if he knows that you want to be in control most guys will give up that control because they think it's damn sexy when the woman gets aggressive. So you must just force his hands down and go "Stop it. I'M pleasuring YOU." The reminder that you're in control and that you're doing it in order to give them a great experience often works. Otherwise, you might as well just let them throw you down and give you one helluva good fucking and then try again at another point when he has a little bit more of an idea of what to expect. Or, if he's willing, you can tie him up.
The answer to #1 is a little more complex... see when a guy is hard it's pretty much assumed that they just want to stick it in and go. And I've never seen anything to really contradict that. But, if you tease them and make them wait a little longer, then it becomes much more interesting for them. More blood rushes down to the penis, they become even more aroused, and their balls actually often tighten. It's a fallacy that women are the only ones whom foreplay can effect, if guys were able to hold out for longer during the foreplay they would find that it definitely increases their pleasure as well (and there are some smart fortunates who figured THAT out a long time ago!).