So a developer bought the property next door, what do I do?!
Do a videotape of every inch of your house, inside and out, to document the current condition.
Line up a structural engineer to walk through your building and submit a written report on the condition of your building, with careful attention to possible problem areas for you to watch.
Line up a good real estate lawyer, without ties to developers or situations that could lead to a conflict of interest.
Check with your insurance company to make sure your coverage is up to date for replacement cost (although the neighbor developer is supposed to be covered).
You can also send copies to the Buildings Department Commissioner (cc the letter) also send a copy to your lawyer if you can afford to have one.
Try contacting the Public Advocate (Betsy Gottbaum): http://pubadvocate.nyc.gov/about/contacts.html
and writing to the state Attny General (Elliot Spitzer): http://www.oag.state.ny.us/contact.html
I really think contacting Gottbaum and Spitzer is a great idea. It's an election year for Spitzer, so go for it.