Does anyone know a free tool that monitors my internet traffic and logs it in a day-by-day overview?
I'm currently using iStat menus but the download meter resets itself after each reboot plus it doesn't offer an activity log for the previous days.
The Tomato firmware for compatible routers has all sorts of logs and graphs for throughput like you're looking for. See their screen shots and documentation online at: http://www.polarcloud.com/tomato
One compatible router on NewEgg: