CapSavvy is a tool that can retrieve your data transfer usage from most independent ISPs and displays it in your system tray
CapSavvy is © Adam Zey, Darryl Tam http://www.dslreports.com/forum/r29128976-CapSavvy-v4-3-released
This is not an official repository. I only include it here because I modified it to make it simpler to work with CapSavvInator. See the above link for the official download link (which includes source)