There's a script that handles image gamma in the scene that  you can access through your Scripts menu.  It's called "Image Gamma."  I can't remember where normal people have it (I customize my Scripts folders), but it will give you a list of the images in your scene and what they're plugged into.  You can usually tell what an image is for by it's name, but if you can't, what it's plugged into should tell you.  Everything that's a black and white intensity map, you should set to gamma 1.  Bump map, specular map, trans map, displacement map, masks, etc.  Anything that controls a value rather than a color.