DigiTech iStomp
In the flourishing world of iOS hardware accessories, the $229 DigiTech iStomp might be the coolest.
The iStomp is a guitar effects pedal lets you download new pedals right from your iPhone. The app comes with ten pedals out of the box, and additional pedals are available as in-app purchases, with a demo period so you can test the tunes before you commit.