Definitely, in general, my acoustic guitar. There's nothing for me like the sweet sound of an acoustic, steel or gut.
For a particular brand item, I'd have to say my little Yamaha dd55 digital drum kit. As an able drummer with no room at all for a kit in my studio, I've always been frustrated with loops and drum machines. The cheapo 55 has many limitations but no direct competition, and I now enjoy hearing my drum parts, ones that I actually played. A very cool toy.
J.