I don't sleep well on closed cell pads alone, so here are some lightweight options that have worked for me:
1. If you like your Therm-a-Rest, take a look at MontBell's line of self-inflating pads. You can add a closed cell pad for a little extra softness, or, like me, add a dual foam mat for pure luxury. My UL 90 and judiciously trimmed foam mat add up to a total of about 18 ounces.
2. Combine a thin closed cell foam pad (like the Gossamer Gear ThinLight) with a lightweight air mattress like BA's new Clearview. The combination offers insulation, pack structure, and a very comfortable night's sleep at a minimal weight penalty (16-18 ounces).
Of course, both of these options are quite a bit heavier and more expensive than Joshua's Gossamer Gear pad combo.