Does anyone know if there's a way to tell the actual amount of damage that is done in an attack? Something that shows how much damage is actually received after armor, resistances and all that? I'm really curious to see how much damage different weapons actually do against different types of enemies.

Maybe a log or maybe a damage number showing up on screen after an attack.

I wish

No, but if you are on PC, you can open the console, click on the enemy and use "getav health" command on him before and after shooting him

But maybe a mod like this will come around: http://www.nexusmods.com/newvegas/mods/59528/?