This fantastic shirt, from ThinkGeek blows the headphone jack t-shirt and the Wi-Fi t-shirt out of the water. It features seven drums, and an inbuilt speaker. Each drum has a different sound.
There’s an awesome video just over the jump of it being played, but I could seriously see this being used on stage. There’s adjustable volume too, with the top volume being “really loud”, so you can disturb your neighbors all around the house, not just when you’re at your real drum kit.