The lungs of mammals and reptiles are pretty similar to each other. The main differences are in the ways the animals expand their body cavities to draw air into the lungs (mammals using ribs and diaphragm, and reptiles using ribs only). The lungs themselves are pretty similar.
The lungs of amphibians are very simple structures, just air sacs with no internal structure. And many amphibians have no lungs at all, breathing entirely through their skin and mouth linings, or breathing water with gills.
However, birds have lungs that are quite different from those of other animals. The biggest difference is in the air sac system. The lungs of a bird do not expand and contract, as those of a mammal do, but the air sacs expand and contract as the bird breathes. The arrangement of ducts between the lungs and various air sacs enables air to move through the lungs always in the same direction, unlike the in-and-out flow of air in a mammal's lungs.
There are other complicated and subtle differences. See http://en.wikipedia.org/wiki/Bird_anatomy#Respiratory_system
Also, the air-breathing organs of fish that breathe air are quite different from those of mammals, but they are not true lungs. The lungfish have an air bladder somewhat like that of an amphibian, and the labyrinth fish have a modified structure of one set of gill arches that is cabable of exchanging oxygen from air. See http://en.wikipedia.org/wiki/Anabantoidei and http://en.wikipedia.org/wiki/Lungfish