As we all know Disneyland and all other Disney parks are constantly changing and "keep moving forward" like Walt Disney wanted. So, like he said, the parks are never complete. And that means the attractions change. Some mainstays, like The Pirates of the Caribbean, It's a Small World, Walt Disney's Enchanted Tiki Room, The Hall of Presidents, The Haunted Mansion, The Carousel of Progress, The Jungle Cruise, etc, will always exist in some form in all to at least one of the parks.
But some have and will change or gotten rid of completely, like Mr. Toad's Wild Ride, ExtraTERRORestrial Alien Encounter, Mickey Mouse Revue, America Sings, World of Motion, Goofy's Barnstormer and many others. These are the extinct attractions. Thanks to the internet, memories of these attractions that would otherwise be forgotten still exist. Not to mention, Imagineers often put homages to the old attractions in new ones (which reminds me... there should totally be a "list of homages in Disney parks" page here). So if you've ever been to a Disney park in the past and have been on any extinct attraction or two and have fond memories of them, share it here. I'd love to hear them!