I've been meaning to get down to the Chris Jordan show at the Yossi Milo Gallery, which should be really interesting (even though the prints involve ink being ejaculated onto paper), and if you catch that, you'll be in the Chelsea gallery district, so you can catch a few others, and then be sure to swing up to the John Stevenson Gallery, which has a great collection of alt-process and gelatin silver prints. There are a few listings to see what's going on, but I usually just pick up _The Village Voice_ when I want to go gallery hopping and check the photo listings.
In addition to the above suggestions, right now there is an island designed by Robert Smithson floating on a barge around Manhattan. I've been hoping to get a shot of it from my apartment. If you google it, you should be able to find an approximate schedule.