This video (Spanish) corresponds to a talk offered during the last RootedCon in Madrid and published by the pentester.es blog. It shows different techniques to perform pivoting through systems in a pentest.
José Selvi - Unprivileged Network Post-Exploitation (Rooted CON 2011) from rootedcon on Vimeo.
I found particularly interesting the mention of the command line kung fu blog.
Props to Paul Asadoorian, Ed Skoudis, Hal Pomeranz and Tim Medin :)
At the end of the video, there is a nice demo that uses some shell fu to discover servers in the internal network and setup the forwards in Metasploit. Sweet!