Magnesium sulfate / potassium sulfate / sodium sulfate
"Just had my 1st colonoscopy using Suprep. Ok, here's the deal: It tastes really awful. Really, really awful.  By far, the absolute worst thing I have ever tasted.  One half hour after the first dose   32 oz of water and apple juice, I projectile vomited.  At one point, my system was being flushed from both ends, which indicated that it actually did work.  Oy.  Relief.

I was unable to finish the next morning's prep without having a violent reaction.  I vomited almost immediately about 5 times.  Was completely unable to keep this stuff down. 
Still, apparently, I was cleaned out enough to go ahead with the Colonoscopy. If there's an alternative to this horribleness in 10 years, sign me up!
Also- what's up with the price? Outrageous."