Cheap, light.....and cheap. You can get these at Walmart for about five or six bucks. The best thing about them is the ability to cut them to whatever size you want. You can even trim the corners to a "mummy" shape to save even more weight. I cut the bottom off one, use the 3/4 as a light-weight summer pad, then use the cut-off bottom as a fire-side seat. As SB said, this is also very good as a pad under a Thermarest or other self-inflating pad.....especially in winter.
This is exactly what I use. There is no need to go and spend a bunch of hard earned cash on some stupid blow up pad that might pop as have two of mine that were issued to me as a solider in the U.S. Army. This is a great option beacuse not only do you not have to blow it up ,when your burnt out from your amazing trec to the top of the world, nor do you have to fret about getting a new one if you happen to loose it in a storm.You might suffer because of the cold but you would any way. The other grerat thing is as stated in the other comment's, you can modify it. I like taking 1/3 off because I am a minimalist. The other thing is that it look's cool to have it straped to you because every one you see know's your out there having the time of your life,you are living!
Light, indestructible, and waterproof. It also stops the heat/cold transfer to the ground. I've popped two 50 dollar thermarests and it isn't worth it. These pads arent that comfortable but they take the edge off uneven ground and sharp rocks and pebbles. Don't spend the money on an expensive pad, save your money for more gear. This pad lasts forever. I have had mine for 10 years. I see these pads selling cheaper than the 17.00 price listed here. Check walmart or other camping departments of the super stores for really cheap prices.
I love my blue pad. It is thin and not very comfortable, but it has gotten me through a lot. It is 8 years old and I've used it probably 50 nights in the last 2 years: snow, wet, glaciers, rock, sand, everything. I tore it a little with my crampons a few weeks ago-it didn't deflate. It is durable and cheap. Rolls up pretty small and I can just stick it outside of my bag. Mine is only 1cm thick, and so is not that warm.
I might switch to a Z-rest in the near future for the increased r-value.
If you are low on cash one of these will do in a pinch. Probably best value for money you can get-1/8th of a price of a thermarest.