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Shawm, Serpent, Sarrusophone, Racket, Aeolian Harp, Stierhorn, Slide Trumpet, Hardanger Fiddle (not very common outside Norway), Nyckelharpa (not very common outside Sweden).

Since you can play guitar maybe a lyre would be something easier to try and learn.

It has such a beautiful sound.

Flageolet (tin whistle) - pretty common in Ireland but less so elsewhere, and VERY portable.

Northumberland Pipes maybe:

http://www.youtube.com/watch?v=4cIqRyuG3jw

How about a Badgermin?

http://www.youtube.com/watch?v=bSnZzlFwUC8

How bout Banjo!