netcat

http://www.g-loaded.eu/2006/11/06/netcat-a-couple-of-useful-examples/
http://www.datastronghold.com/articles/3.html

Port Scanning (check if TCP ports 80-90 are open)
nc -vzt 192.168.0.1 80-90

Banner grabbing
nc -v -n 192.168.0.1 80