This show is a very good one, but it barely gets any recognition. Go figure. It's on the Fox Reality Channel (not exactly known for quality programming).
The basic premise is that nine people are put in tiny rooms in solitary confinement. They are put through endurance tests (such as extreme cold, extreme dizziness, loud noises, etc.) The contestants can press a big red button any time they wish to quit. But the first person to quit in each challenge is eliminated. The interesting thing is that they don't know if anyone else has quit yet, so it's all about them reaching their own personal limits.
Fox Reality Channel is going off the air at the end of March 2010. Season 4 of Solitary will air sometime before that in 2010. Please support it (I would, but I don't have that channel. I've watched the first three seasons on Hulu). Maybe it will get picked up by Fox!