Check out
BeefyBoard, it's an iPhone soundboard that lets you create your own soundboards and save them to your iPhone. It also works on 2nd generation iPod touch as well. The cool part is you can upload the soundboards you've created and download other peoples soundboards as well.
There is a built in drum soundboard, but you can also create your own if you want.
It also has skin support so you can create and upload skins at
http://www.beefyapps.com and then swap out the default skins on the buttons to whatever you want (a drum skin for example).