Some VPSes charge for outgoing network traffic per month, so how can I check on the Unix command line how much outgoing network traffic has run so far this month?
An ASCII graph where X is days and Y is traffic would be nice bonus :)
You need to log it before you can display it. A popular logging and graphing tool is MRTG.
(Posted this as a comment at first, but I guess it is a full answer in some respect.)