Hmm I'm finding this thread very interesting. Had an s3 since June and it has been brilliant. I don't really hammer it often so an average day is reading emails, a little surfing and the odd text MSG. With that in mind, I easily get at least 48 hours from a charge. I do have wifi, gps and Bluetooth turned off permanently but have sync and mobile data on.
In the last 2 days I have been getting the problem the OP has. Battery drains within a day with no use, somewhere around 8% an hour in standby. Battery usage shows this to be Cell Standby.
As far as I can work out I haven't changed anything. My apps have been updated and i have installed a couple of new apps but deleted those (adobe air and sky sports centre) with no luck. The only app I can definetly recall has updated was light flow lite but turning that off completely does nothing to improve it.
Running android version 4.0.4 at the moment in the uk. I don't have K9 mail installed (I think?) and have made no changes to how my email clients work. Very frustrated with this. I turned the phone onto airplane mode and it went back to normal, I turned off the sync option on the drop down menu and it still drained quickly so seems to be something to do with the signal perhaps?
Been loving using my s3, want it back to how it was!