Originally Posted by drode
If you have an untouched background layer...
I always duplicate the layer first thing and leave it on top of the stack, that way I just have to click. Also, keeping an original layer in the same file can come in handy if you ever need to grab data from the original image to do something (like cloning original data in if you notice a heal scar late in the process).
It would also be an easy matter to record actions to turn that layer on and off, provided you name the layer the same thing every time (I always name it "Original") but I would make sure that no layers are selected when you are recording the actions, you don't want it to record as "Show Current Layer" instead of "Show Layer 'Original'" You could assign the actions to neighboring keys so you can toggle the layer on and off easily.