Some of my favorite CGI work used in films are in Frank Millers '300' and 'Sin City'. Both films used computer generated backgrounds in mostly all of the shots. Both films were shot on blue screen filmed on high definition. In 'Sin City' the buildings were all created in 3d then textured to look photo realistic. In '300' all the skys and landscapes were CG, which is why they look so spectacular and over the top.