Cornell has several sites that are helpful in finding old classmates and other alumni.

The best place to start is at Cornell's Alumni Website:
http://www.alumni.cornell.edu/

An on-line alumni directory can be found at:
http:// www.alumni.cornell.edu/services/Find.html

While you are there don't forget to update your address with Cornell:
http://www.alumni.cornell.edu/services/addressupdate.taf?function=form

Engineers might also be interested in the Cornell Society of Engineers: http://www.cse.cornell.edu/