The rack is the best. I was put on one in a dungeon back in 1999. It was scary, but I was so turned on I thought I would die. I was stretched very tight, but the dungeon's mistress knew how tight I could be stretched safely. She was just shocked to see my husband tickle my feet, belly, armpits, breasts in that situation.
Another variation of the rack in that dungeon was the wheel. It looks like a small (five feet high) paddlewheel like boats used to have. There is a ring on the floor in front of this wheel. My ankles were tied with a rope that passed through the ring and my hands were tied over my head and fixed to a hook on the wheel. The wheel was turned with a crank that stretched my body with my back bent against the wheel, my arms at the top of the wheel and my feet off the floor with my toes pointing straight to the floor. It was sexy. Being naked and stretched as tight as possible always is sexy. But it was rough on my shoulders. They were sore for days after being on the wheel for so long (20-25 minutes, I was told).