I'm looking for one using Advanced Task Killer. Nothing out of the ordinary shows up on the "What's using the battery" section of Settings...
From what I have seen, they usually don't. I think programs are just kind of hanging. They aren't able to sleep, but don't use much battery either ( It's just the fact that everything else continues to run full tilt since the phone is not sleeping that causes the battery drain. )
I recommend starting with the usual suspects ( Calendar, Facebook for HTC, Advanced Task Killer, and any apps you have downloaded. ) and just working down the list of non-essentials. Do it 1 app at a time, put your phone to sleep. About 10 mins later wake it and look at the awake time to see if it changed. When you press the power button, it should go to sleep within about 2-3 seconds of pressing the button normally.
I definately recommend getting rid ATK and anything like it. Time and again I have heard of them causing problems. Use the androids system for closing apps IF you have to force anything to close. Always try to close an app from inside an app...unfortunately generally when something is hanging in sleep, it won't properly shut down either. So, again, use the built in method instead of ATK or other task killers:
menu->settings->applications->manage applications ( not running services ). Press menu->filter and select running to only show running apps, and close them.
NOTE: For a couple things, like calendar, you might need to also close the service which is under 'Running Services".
If you can't find the culprit, check back and we'll see what we can do.
