Just putting this here so I can find it easily in the future.
I wanted a way of seeing how much traffic was going from my computer to other hosts. Actually, a room-mate was downloading a file from my computer, and I wanted an easy way of monitoring the progress, and seeing when it was done.
iftop did exactly what I wanted.
Thank-you to noah’s packet sniffing page for the heads-up.
For each host, you can see outgoing bandwidth, incoming, and a barchart of the relative bandwidth to each host. The figures are pretty much real-time, updating once a second or two. For example, I didn’t want to have to use tcpdump, then process a dumpfile. I just wanted a realtime display of bandwidth to each host, and iftop does exactly that.