Tuba! Tuba! AND trombone!

Seriously, though... Dulcimer? You seem to like concertina, and that's always an option. Other than that, like Susan said - what sound do you like? What are you aiming for?

If you want to stick with the familiar, you can also just try variants on the instruments that you already play - pennywhistle lends itself somewhat towards recorders, irish pipes, and (I've been told) clarinet. Bodrhan lends itself to... er... well, beating on other things.

M