well, i would check online for the info on the DA's office, the DA in manhattan is a great place to summer. I would also do a search for all of the federal and local judges in the city as well. If you are at NYU/Columbia/Forham, you should have a decent shot at a federal thing in the SDNY. Your school should have a simplicity website? possibly, and it has a listing of all the jobs in the area. If you are at any of those three, I would suggest going onto nalp and doing a mail merge of the firms. It couldnt hurt. Also, the career development office should have packets of job information. I know we have several little minature booklets full of public interest jobs available for the summer, and government internships. I would venture to say that your school has a simplicity site which is a great way to find jobs.
I applied to everything DOD or DOJ, federal internships, and every firm in the city, and ended up with something decent. So, NALP, Simplicity, and any handout you can grab in the CDO, in addition to DA's offices, public defenders office, and all the clerkships. Even in the top 15% I had limited interviews and I applied to 200+ places (granted many were firms and many had atrocious spelling on the cover letters, but still). So, apply to as much as you can. Wait till you get grades though, they really help you stand out. That is, unless you are wanting to go home and work over the summer and am not from NY in which case it is better to apply earlier rather then later so they can squeeze you in for interviews over the break.