In terms of animals that have disappeared that capture the imagination, the dinosaurs would have to take the top honors here. I cannot imagine how millions of children conceived of their own imaginations and sense of wonderment without reflecting on the strength, power, and disappearance of the dinosaur. Childhood seems to be consisting of a "phase" where kids feel T- Rex was the best dinosaur or that Triceratops was the most "awesome" dinosaur. The very idea that these animals ran the show billions of years ago and then were almost instantly wiped out captures the imagination and proves that even the most powerful of creatures faces a finite life span. Although from a child's point of view, this might not be fully articulated, it is completely felt.
The list of animals that have gone extinct goes on and on. Not only are there many different kinds of animals that have gone extinct but there are many different kinds of plants as well.
Like the previous responder stated, dinosaurs are type of amazing animal that has gone extinct. For example, the Tyrannosaurus Rex went extinct about 65 million years ago.
In 1883, the Quagga went extinct. This magnificent animal was half zebra, half horse. This is a very famous animal that once lived in Africa. It's front half looked like a zebra and bak half was brown.
Another amazing animal that has gone extinct is the Thylacine. It went extinct in 1936 and is also known as the Tasmanian Tiger. It was natively found in Australia and New Guinea.
There are so many different kinds of animals that have disappeared from the earth (that have become extinct). I would suggest that you use Google to find a real list of them -- just type in "extinct animals."
Of course the most famous kind of animals that has become extinct is the dinosaurs. The dinosaurs were a hugely successful kind of animal with many species. They died off around 65 million years ago.
Some species have become extinct in modern times. For example, the moa, which was a large flightless bird in New Zealand is extinct. So are passenger pigeons which once traveled in huge flocks in the United States.