One correction: EVERYBODY here is awesome!
For outdoor markets in Manhattan selling "stuff" (as opposed to the Greenmarkets selling food): there's a big flea market on the weekends on 6th Avenue (what the rest of the world calls Avenue of the Americas

) a little bit above 23rd Street, and a smaller one on 38th or 39th, west of the Port Authority Bus Terminal.
BUT: it could be a lot more interesting to take the #7 train to Jackson Heights in Queens and just walk along Roosevelt Avenue, under the elevated tracks. You'll get Indian, Bangla, all kinds of South and Central American -- a huge mix of different cultures. Or go up to Arthur Avenue in the Bronx, for a REAL "Little Italy." Or downtown Jamaica (also in Queens).