Task of counting traffic is kept alive for years by arms race of connection speeds and sizes of those bulky video files. :) On large scale knowing how much you spend in total is fine and there are numerous excellent utilities for that.
However for more limited connections, such as slowly emerging mobile Internet, counting each megabyte may be critical. NetLimiter is excellent utility that focuses on keeping extremely detailed statistics of traffic consumption.
What it does
NetLimiter has interface that reminds of process managers but instead of performance stats it is focused on network bandwidth.
It shows current downstream and upstream speed for each process. Tree can be further expanded to show speeds for specific IPs.
Real time monitoring is nice but real power of NetLimiter is very detailed statistics. It remembers and can show what traffic specific process consumed in specific time period. Reports can be viewed in interface or exported in XML (manually or on schedule).
Free Monitor version only keeps stats but there are also advanced versions that allow to shape bandwidth by setting limits or guaranteed bandwidth for applications. That’s where Limiter part of name comes from actually.
App could use some kind of floating indicator so it could show current speeds without having to open interface. Other than that it is excellent freebie for keeping very detailed traffic statistics. Installs deep into the system so very not portable.