NetHogs, iftop, Monitorix
Please see the following link: http://www.tecmint.com/command-line-tools-to-monitor-linux-performance/
read on if you want, but the link should be enough :-)
I think the first 14 or 15 were really handy to have. The reason I came to this, is because I share my network with the buildbot slave, and I would like to be able to log onto the slave via ssh and see if it is actually using the network before I decide to do something that might be network critical. So while I have no gui on that slave, no monitor, no mouse, and yep.. no keyboard, much of the applications will have to work in the terminal.
Though we do actually have htop, I can't really see from that if the network is being used to upload a fresh built packlage such as a large kernel source. And htop doesn't actually show me that I can't turn off the power to this machine without causing failure in a package being uploaded. usually I can go to the buildbot page, look at my slave, and see if it is currently building something, and then I know not to turn it off yet, but that doesn't even show me that it still uploading.
The build process for example may have ended 10 minutes ago, however the package may still be uploading to the vlcore. Unless I am actually looking at light activity on the NIC or modem, I cannot easily tell. Hense I feel the need for something like the 3 apps listed above the link, though for my purpose iftop seems to be the top of the list.