In the days of Unlimited Plans, bandwidth monitoring may be passe, but it is still helpful to keep an eye on the amount of bandwidth you consume. There are many bandwidth monitoring tools available but most of them are either bloated, not free or not user friendly. If you want a free, small application to monitor your bandwidth look no further than Bitmeter. Though not CPU intensive, Bitmeter does consume a fair amount of memory (22MB when i last checked). If you are on a pay per usage plan, you are going to love the ISP restriction feature of BitMeter. You can put in your montly quota of traffic and can configure BitMeter to alert you when you have a cosumed a certain percentage of that quota.
The installer is 1MB and needs .Net Runtime (23.1 MB). If you are on a slow connection .Net Runtime is usually contained in the CD's you get along with CHIP and DIGIT