I like my thermorest roll-up pad. It's the short one, only goes from my head to the back of my knees, but that's plenty. It's surprisingly comfertable for how thin it is, and it's not too expensive. Best piece of gear I've bought so far. I wrap it up with my sleeping bag for easy storage. It does tend to slip around a bit, some suggestions to prevent this I haven't tried are velcroing it the tent floor, putting a shelf liner between it and the tent floor and even adding dots of silcon caulk to the tent floor!

Some of my fellow hikers are larger men, at least one is a bit overweight. (I'm 5'8'', 140 lbs) These men tell me that the thin thermorest pads aren't sufficent enough padding for them, as their weight compresses the pad to the point where they feel like they're laying directly on the ground. These men use the inflatable kind and are quite happy with them I believe. One however did tell me his inflatable has a slow leak now and by the middle of the night he wakes up to find he's on the ground again.

As much as I love my thermorest, I think I might be upgrading to an inflatable soon (at least for the colder months of for whenever I get to a trip longer than a few days).