Shockwave (Six Flags Great America) - When I was younger it was always cool how that coaster dominated the front landscape of Great America.
Deja Vu (Six Flags over Georgia) - Awesome ride, glad there's at least two of those left in America. Wouldn't say its completely defunct yet, but it's been sitting in Brazilian storage since 2009 so that's good enough for me.
Jaws (Universal Orlando) - Not a coaster, but still really shocked they scrapped this for another Harry Potter development. This was, hands down, my favorite ride at Universal until Revenge of the Mummy arrived. It was such a classic and always delivered a unique ride experience. My saddest loss in the amusement industry.