If I remember correctly the problem you were trying to fix was boominess from bass wasn't it? If that is the case you will need auralex bass traps. These are triangular foam pieces that go in the corners of the room. I would start with bass traps to get clear bass monitoring and then move on to the acoustic panels to treat the wall behind the speakers.

I just bought the Auralex Max-Wall 420 system. Is is awesome, kind of pricy, but it is movable, fits on stands. I didn't have to glue or nail anything to the wall and it looks very nice too (may be not nice enough for a living room though)

If you look at the panels that show on my studio pictures, I used large framed cork bulletin boards, glued the foam on the back of these boards. This way, I didn't have to glue or nail the foam directly to the walls. I then just put up these boards on the wall using one nail. I am sure cork board it self also has sound absorption qualities, not sure by how much, but those boards also helped. I will be using them in my vocals booth that I am currently working on.