Unfortunately the only way to really meter the traffic is to have a router that supports SNMP. Your run of the mill home routers aren't likely to have SNMP capabilities (but if you have a linksys with the linux firmware, I believe it adds SNMP support). Your options really are looking at the lights, or putting a linux box between your internet and your network and then using it to measure usage with a program like mrtg. You can also use tools like tc to set limits on connections to certain address ranges.