One of my favourite backgrounds for ATCs are using acrylic paint. I love my ATCs to be sturdy and sometimes I use regular thin chipboard which I cut into the ATC size of 2 1/2 inch by 3 1/2 inch. Thereafter - I just give it a coat of acrylic paint. Then its ready to be stamped on.
Here I have stamped and embossed using white UTEE and then further distressed the ATC using the Stazon ink. I love this effect - hope you try it too.