Various useful lsof options:

To view files open by a particular PID:
lsof -p pidnumber

To show processes and the port they are running on. This is a great command to find out not only process and port, but also the command and the PID.:
lsof -i -nP # The -n does not resolve the IP addresses and ports to names.

Source: http://sial.org/howto/debug/unix/lsof/