Main problem with Ducks is they poo. A lot. Everywhere. I had a pet duck (well it turned out to be a drake) but we were on a large block. Alright if you have a permaculture garden, but you might want to fence off your outdoor living area so you're not stepping/sitting in it all the time.

I'm with the others...How about a guinea pig or two? You could always go to the pet shop for a trial allergy run before commiting.

Otherwise, go reptilian - a tortoise is interesting.