Hi,
as from title, getting about 1.2 terabytes per day.

Its not doing too much harm as I am running nginx, so as long as simultaneous connections stays below 10000, server load is managing to stay below 1.

What command can I run through SSH to identify top IP addresses by bandwidth usage???

I am running centos 5 based on linux

awaitng reply !

check your logs or script which u have installed like google analytics or statcounter to identify those

what kinda site is it? i got threw that in a day but i run a streaming site.