Radiator covers can be made to many different designs. Two are shown here, painted and unpainted, made of MDF with perforated grilles, and one is made of oak with a brass grille. If you look in the fitted office furniture section you will find a radiator built in to a bookcase with a woven oak grille.
Bay window seats can be made to fit any shape of window bay, and can even have radiators covers built into them. This particular one is made of cherry, with leather upholstery.