Who can I contact if I get broken into?

If you're connected to the Internet, you should certainly get in touch with CERT, the Computer Emergency Response Team.

To quote the official blurb:

The Computer Emergency Response Team (CERT) was formed by the Defense Advanced Research Projects Agency (DARPA) in 1988 to serve as a focal point for the computer security concerns of Internet users. The Coordination Center for the CERT is located at the Software Engineering Institute, Carnegie Mellon University, Pittsburgh, PA.
Internet E-mail: cert@cert.sei.cmu.edu
Telephone: 412-268-7090 24-hour hotline:
CERT/CC personnel answer 7:30a.m. to 6:00p.m. EST(GMT-5)/EDT(GMT-4), and are on call for emergencies during other hours.

...and also, the umbrella group "FIRST", which mediates between the incident handling teams themselves...

[...] FIRST is actually a very viable and growing organization, of which CERT is a member. It's not actually true that, if you're connected to the Internet, you should call CERT only - that doesn't do justice to the many other response teams out there and in the process of forming.

NIST is currently the FIRST secretariat; we maintain an anonymous ftp server with a directory of FIRST information (csrc.ncsl.nist.gov: ~/pub/first). This directory contains a contact file that lists the current members and their constituencies and contact information (filename "first-contacts").

While CERT is a great organization, other response teams who do handle incidents on their parts of the Internet merit some mention as well - perhaps mentioning the existence of this file would help to do that in a limited space.

The file mentioned is a comprehensive listing of contact points per network for security incidents. It is too large to reproduce here, I suggest that the reader obtains a copy for his/her self by the means given.