Re: Other than drums ....
+1 for Cello. If I wasn't a drummer I'd be playing the Cello right now. I think it's appeal is much like the drums in that from one instrument, such a diverse array of sounds are possible. I also like it's soothing nature and is quite the break from the violent nature of drums. Bach Cello Suites by Pablo Casals is one of my top 5 "must have" Cd's, so beautiful.
I would go out tomorrow and buy one but I think if I did my drum progress would come to a halt and I don't want to spread myself thin.