well nice question :

from GF:
Don Vito's Desk and chair
Don Vito's Hat from last scene playing with his grandchild

from GF II :
the rug young don vito gets from clemenza
and the boat fredo got killed in

from GF III :
the maroon sweater Don Michael was wearing when he had his stroke (Just When I Thought I was out,, my fav scene as you can see from my sig )