A pad like this one–self-inflating open-cell foam, full-length, 1.5 inches thick–has been a mainstay of backcountry campers for years. It's tough, comfortable, warm, packable, and relatively lightweight. And this one is particularly affordable.
We also like the Trail Pad's waffle-style punched foam, which saves weight and bulk, as does the semi-rectangular shape–rounded at the corners and slightly tapered toward the foot. And it comes with a generously sized stuffsack (which is more rare than it should be). $69; 1 lb. 6 oz.; 20"x72"x1.5"; ems.com