Also handy are lsof, netstat and fuser.
netstat -anp will show you which process under what PID have open what ports: another way of seeing what services are running,
lsof -p <PID> shows you all the files and sockets a process has opened,
and fuser </path/and/filename> show who has that file in use: kinda handy when you're trawling dir's.
Also if you're concerned with running local or net services you don't need you can dis/enable them using ntsysv or linuxconf.
If you've got time please have a look at CERT UNIX Security Checklist v2.0