For years I've belonged to a big health club that has rows of exercise contraptions. I use them regularly, and while I do, I wonder how you could make that sort of mindless exercise more interesting.
One idea is to have some sort of RFID device on your gym ID card, and keep it with you when you work out. Each exercise machine would automatically recognize your presence and access your history. You could do a lot of interesting things with that technology, but the idea that interests me most is a graph of how many pounds you are moving per week, using any subset of the machines. The idea here is that it wouldn't matter what muscles you were working so long as you moved more weight this week than last. And you could watch your tally increase with each repetition.
My theory is that although this somewhat random approach to weight training wouldn't have targeted results, it would bias you toward working your largest muscles, which is a good thing. And it might encourage you to use lots of different machines instead of just your favorites, especially after your favorite exercises fatigue specific muscles.
My other exercise idea is to make video game controllers that weigh five pounds apiece, shaped like small dumbbells, and create games where you steer the action using two controllers, one in each hand. For example, imagine aiming a big gun in a video game, or pumping your arms to make your character run, or leaning your digital motorcycle or skier to make him turn. All the game action would require moving your hand weights. An hour of that per day would make you look ripped, at least from the waist up. And it might be more fun than pushing buttons.
I think it's great that you can listen to your iPod while exercising, but weight training is still mostly a technology of the 1800s. It's time for some updating.