What used speaker would you buy with $20,000-$35,000 and why?

I'm closer to the 20,000 part, but if I get stretched i would like to know higher recommendations. Remember, this is on the used market - not retail. I'm even interested if you think I should make a huge jump (say to 50,000), but I want to know what justifies that jump. I'd like the best bang for the buck and even the worse bang for the buck. Are there speaker lines that are totally overlooked that sound wonderful in this price range that I need to be exposed to? I may go higher, but lets start there.

PS Let's just assume the upstream equipment is adequate to drive any recommended speaker. We are not limited by upstream components.