How about a single speed cross bike like mine? It's a fixed gear cross bike that I use to commute, run errands on and do charity rides, and plain ol' riding. Plus I live in Manhattan.
If you plan on riding the hills of NJ up to Piermont and Nyack, you might want the geared cross bike. If you plan on riding around NYC and locking up a lot, nothing wrong w/ a single speed and fatter tires (28 or greater). Your best investment will be in locks. Get good ones (plural).