How can I tell what is really draining my battery?
Try out an app called Watchdog.

It monitors your apps and alerts you to anything that is using your cpu excessively. It might help unless it something that's draining consistently at a low level.

I'd have to agree that it doesn't sound like you have a problem. Battery life seems good.

Juice Plotter is another battery monitor that you might be interested in and its companion app Juice defender might help squeeze extra life out of your phone as it can switch off your 3G off unless needed.