Art Gallery: Masaccio: An Online Gallery Featuring many Hi Res images of the artist, featuring the Brancacci Chapel frescos and the tribute money.
Artchive: Masaccio: Images (details) of the paintings.
Life of an Artist: Masaccio di S. Giovanni: Biography of the painter as recorded by Giorgio Vasari. Includes an image gallery.
Olga's Gallery: Masaccio: Collection of the artist's works with a biography and historical comments.