Art Cyclopedia
Artcyclopedia: Chronological Listing of Landscape Painters
ArtCyclopedia's chronological list of landscape painters from the 16th thru the 20th centuries. There are links to the artists' biography and works.
ArtLex
Art Lex: Landscape
A very nice website with a definition of landscape and several examples of landscape paintings and photographs. Provides links to landscape art from specific historical eras.