Joseph Mitchell is one of my favorite New York writers; I find myself pressing his essay collections into the hands of my friends when they come to the city. "You'll love it! And maybe you'll start your own Oral History!" The Oral History is a reference to the project at hand in Joe Gould's Secret, which you could start with if you want a quick taste of Mitchell's work, or Up in the Old Hotel offers a good survey of his pieces from the New Yorker; The Bottom of the Harbor is also stellar (though its essays, I believe, are all included in Old Hotel).
I'm revisiting My Ears Are Bent, a collection of his pieces for the World-Telegram and the Herald Tribune -- work that came before his New Yorker period. The essays are a little rougher, less polished, but no less enchanting. It's the way he captures people that really stands out; and it's no wonder. Mitchell writes:
I believe the most interesting human beings, so far as talk is concerned, are anthropologists, farmers...and an occasional bartender. The best talk is artless, the talk of people trying to reassure or comfort themselves, women in the sun, grouped around baby carriages, talking about their weeks in the hospital or the way meat has gone up, or men in salooons, talking to combat the loneliness everyone feels.