I think the quintessential Woody Allen film is Annie Hall, without a doubt. Manhattan is his sonnet to NYC--loved the Gershwin in that one. However, the one I keep going back to is Hannah and her Sisters. I really appreciate the multiple narratives in the film. And at the risk of sounding sacrilegious I really liked Matchpoint and Vicky Christina Barcelona--but his later films don't really feel like Woody Allen films at all. They're good enough to stand on their own.