I'm looking for a program that will measure how much data (in terms of Mbytes) has been tranfered thorugh an ADSL Internet connection (both Upload and Download) for its duration. Actually, what I'm looking for is a program that will make this measurement on any Ethernet connection, both of an ADSL or LAN connection.

I need this because i use a mobile phone as modem, and my ISP gives me a flat rate up to 500 Mb each month. I'd like to check how much I use, so that i don't pay the extra traffic.