BTTF, with a heartfelt recommendation, to folks who haven't tried it yet, to check out Zemeckis & Gale's earlier collaboration, "I Wanna Hold Your Hand." It's sort of a distant cousin of "1941" and BTTF, in more ways than one.
That's a tough one, but I'd probably have to go with "Back to the Future". Although, I also really loved "Gremlins" and as a huge Beatles fan, I always really enjoyed "I Wanna Hold Your Hand" as well....
TV-wise let's hope The Talisman, I have to say I was fairly disappointed with Under the Dome.
As far as his executive produced films go, I'd say Men in Black III, Jurassic Park III, Who Framed Roger Rabbit, The Goonies, ... but not really one that jumps out. I might go with Poltergeist though he did more than produce on that.