It is a very dense city with mostly flat areas in Manhattan...but there are other Burroughs surrounding the island of Manhattan where I will likely live (for cost reasons), which are somewhat hillier. That also means there I'll hit at least one bridge daily as I commute to and from the city proper. So perhaps gears would be better. BUT, on the other hand, instead of using the bridges I might want to hop on the Subway to get across the East River (separates Manhattan from the Burroughs--Brooklyn and Queens.) In that case, I might want something lighter to carry on with me as the Subway system is a maze of underground stairways.
Either way, all, I'm definitely going to buy a bike in NYC, so does anyone know of a respectable/friendly bike shop up there? Perhaps where I could get a refurbished bike?

It's mostly flat except for the hills and valley. Northern Manhattan actually is hilly. So is the Bronx which is part of NYC and Yonkers which adjoins the Bronx. Brooklyn's Prospect Park is up a hill from the water's edge, and Staten Island has a bunch of hills. Queens is kinda flat though.

Recycle a bike. There's a shop in LES and another in Bklyn.

I commute on a SS 'Cross bike. Works great for me.

This would be my advice as well. Get an inexpensive bike and a couple of good locks and you should be good to go.

-DR

im not sure why some people think that you cant ride up a hill on a SS bike...its really not bad, Ive done multiple long and hilly rides in groups of roadies on a fixed gear. for riding manhattan, 44:16 will get you everywhere you need to go, if you feel like you might need more power, drop it down a bit.

SS bikes are just so much nicer to ride. I sold my fixed gear to get a road bike, thinking i would enjoy longer rides more....well now that i have a road bike, i want the fixed gear back. theres a reason, beyond trend, that so many people in nyc ride SS/fixed.

There are also reasons, besides just enjoying superfluous moving parts, that so many don't. Bring your SS/fixed up to the Heights and show me how it can tow 100 pounds of kid trailer up a 25% grade some time.

Everybody doesn't live on the flats, everybody doesn't have quads of adamantine, and everybody doesn't need a single-speed. If you're in reasonably good shape, live in Chelsea, and don't think there's a world above 34th Street, go for it. (In fact, I think it's required.)

If you don't know where you're going to live yet, or where you're going to want to travel, it's probably not prudent to make the decision at this juncture.

+1. If you want new instead of refurb, I'm impressed with Larry and Jeff's on 2nd Ave.

One benefit of a single speed like a Bianchi San Jose is apart from the lower price and lower maintenance, there's less to easily rip off the bike, since everything (wheels, seat, etc) is bolted on. Granted you could probably get a geared bike without the quick-release as well if you're building it up yourself. Still, especially in a place like NYC, making your bike less susceptible to crimes of opportunity can only be a good thing. Of course as a previous poster alluded to, climbing the hill on Broadway between 186 and 181st streets would be an adventure with a single-speed.

Another consideration--just to add to the discussion--I have pretty muscular legs and don't want to build up. In fact flexibility and tone in my legs are goals of mine, not bulk. Perhaps a SS would require harder pedaling in hilly places where I could simply downshift with a geared, saving my legs the stress and reducing the amount of muscle "building."