University of California
Ucmp: Aves: Fossil Record
A very good article on the fossil evidence and the prominent theory on the evolution of birds. Addresses both sides and presents information. Predominently agrees with the pro-dinosaurian point of view.
University of Guelph
Canada's Aquatic Environment/evolution of Birds
A good site that goes over the similarities and differences of reptiles and birds. Good look at the issue from a seemingly neutral view.
University of California
Ucmp: Systematics
A good overview of the radiation within the class through geologic time.
University of Guelph
Aquatic Environments: Birds
A great site for bird lovers or anyone seeking interesting information on birds. Provides links to other bird links such as bird species, descriptions, game and more!
PBS
Pbs/evolution: Birds Arrived Comparitively Late
Good discussion of both sides of the debate over the origins of birds. Presents the recent evidence that seems to lean in the direction of the pro-dinosaur ancestry argument.
Other
Ornithology: The Evolution of Birds
Site provides a good overview of avian evolution debate without taking a firm stance on the dino-ancestry issue. Gives the broad ideas concerning bird origin and evolution.