PBS
Pbs: Nova: The Four Winged Dinosaur
In 2002, paleontologists discovered a fossil in China that seemed to provide a missing link between dinosaurs and birds, and to support the theory that birds evolved from dinosaurs. The fossil came from a four-winged dinosaur they named...
University of California
Ucmp: Are Birds Really Dinosaurs?
A great essay that illustrates how science is done as well as the relationship between dinosaurs and modern birds. Includes a picture to illustrate this concept, and contains many links to related sites.
Other
Natural History Museum of Los Angeles County: Dinosaur Institute: Dinosaurs
The origins, evolution and diversification of dinosaurs through geologic time are described, as well as their portrayal in Hollywood movies. There is also information about how birds evolved from dinosaurs.