SSH
From Jon's Wiki
Harden your SSH, consider these in your /etc/ssh/sshd_config file.
PubkeyAuthentication yes PasswordAuthentication no PermitRootLogin no PermitEmptyPasswords no AllowUsers alice bob carol X11Forwarding no
Use keys, it's the 21st Century now. Also, you can tar-pit wankers trying to hammer their way in. This will drop anyone trying to connect more than three times in 30 seconds:
iptables -I INPUT -p tcp --dport 22 -i eth0 -m state --state NEW -m recent --set iptables -I INPUT -p tcp --dport 22 -i eth0 -m state --state NEW -m recent --update --seconds 30 --hitcount 3 -j DROP