Best Acoustic Carpet and Padding for music room?

Nothing wrong w/ carpet nor rugs, so long as, it stays on the floor(s).
Never on walls nor ceilings...

Carpets and even acoustic carpets are usually not good for the sound. And carpets or SONEX placed on the wall between the speakers is usually not good either. But they SEEM like such good ideas. Even those foam filled Ikea chairs, Puong or whatever, obviously hurt the sound if you ask me.

Never heard of acoustic carpet/pad, but I would suggest looking into what is used in sound studios or anechoic chambers.  You could also research the materials used in carpeting/pads.  I would not be surprised if you were to find that natural wool fibers offer better acoustic properties than man-made fibers, but I have never looked into it.  As a last resort, you could go with the thicker-is-better strategy....shag baby!

I am willing to spend several hundred dollars, but I want a real acoustic carpeting treatment.  There are variances out there in product.  

Go to Lowe's or Home Depot.

A few years back we found some rugs on craig's list--some were free, the others were cheap.  Start with their "free stuff" section.