BitMeter 

This powerful program makes measuring bandwidth usage a simple and accurate job. It allows monitoring bandwidth consumption in order to alert you when pre-established limits are about to reach. Therefore, if your Internet provider is imposing limits for your traffic, you will know when your current traffic quota is exceeded and avoid having to deal with additional costs.

BitMeter is quite unobtrusive and it won’t interfere with your usual daily computer activities. Most of the time, it will display only a scrolling graph that shows the upload and download speed of your connection in real time. This tool is easy to use as its interface is straightforward and neat, allowing even beginners to handle it.

I also like that it includes a comprehensive and handy “statistics” panel that depicts changes of historical traffic data. The data displayed by the graphs or by the “statistics” window can be transformed into a numerical format and exported to standalone files (spreadsheets).

Another remarkable feature is the alerting system that lets you assign alarms for any traffic quota. These alarms can trigger sound notifications or popup messages, and can be assigned when a traffic volume quota is reached or when a specific traffic speed is attained.

As you can see, BitMeter comes with many handy features, and I mentioned only a few of them. It’s a great tool that works like a charm and comes with an unbeatable price: it’s free.