For me it would be the Douglas A-20 Havoc. A major weapon of WWII, flown by the U.S., the British, and Russians. Played a big part in the lead up to D-Day.
I know Kermit has one. Maybe two. But they need restoration. I've also heard of one being restored in... Pennsylvania, I think. But I don't know how far along they are with it. There is one, in flying conditon, in Texas. But they don't fly it any more, due to it's rarity. And, of course, there's the one in the Air Force Museum, in Dayton. But that's mostly a "cosmetic" restoration.
We had a former Havoc pilot - 12th AAF, 47th BG(Lt), 86th BS - in our office, who retired a couple years ago. Jim is a modest and quiet man, with a seriously odd sense of humor (loves the pun), and a lovely wife. Katie was an army nurse, and with one of the first groups into the concentration camps after liberation.
Jim loves to reminisce about the war years, and the A-20. The one thing he doesn't talk about much, is his Silver Star. Awarded for actions he took while leading a mission over Italy. (He doesn't think it was all that big a deal.)
Jim suffered congestive heart failure last spring and is now on 24hr oxygen. I don't want to say he's close to leaving us, but I sure would love for him to get one more look at the plane he loves, in the air, while there is still time.
(If anyone has one, and is listening, the home field is Burlington, WI - BUU. Please give me a couple hours notice before you drop in. )