Wallpaper

• Wallpaper comes in multitudes of styles and thicknesses. Pick a wide wallpaper border and run it over the entire back of your counter, including behind the sink. Make sure it's a thick, glossy paper to stand up to splashes. Choose colors and designs to complement the countertop and walls. Hang it according to manufacturer's instructions, and lay a thin bead of clear silicone caulk along the bottom edge at the countertop.
  
  

Glass

• For a sleek, modern look, get a thick (1/4-inch) piece of glass cut to size from your local hardware store to fit across the area behind the sink. Paint one side of it in solid color to complement the countertop and other parts of the room. When dry, glue the glass to the wall, painted side facing the wall, using carpenter's glue (the paint will hide the glue). Run silicone caulk around all four sides to seal it.
  
  

Wood

• Find a rich, layered style of decorative paneling in oak or another hardwood. Stain it to your liking, and apply one layer of protective polyurethane gloss. Glue it to the wall behind the sink, trimming it around the edges with trim stained and glossed in the same manner as the paneling. Buff the whole thing with 220-grit sandpaper to take off the shine (so the next layer of polyurethane will stick), then apply the second layer. Buff it again, and apply a third layer. Run a thin bead of clear silicone caulk all around the edges and on every seam of the backsplash.