Wallpaper, peel and stick tile, tin tiles, paint, wood . . . Here are some sites for inspiration.
One idea could be a sheet of stainless steel. I have framed art on mine the last 10 years.
One newer ideas of interest to me is a fireback as a decorative backsplash is to use that near the stove cooktop. It was on an episode of This Old House. Depending upon your lighting and decor sometimes a pop of black is really attractive in a room. They come in various sizes, quite heavy need to be mounted to the wall, they used an adhesive mount on TOH.
contact paper or the self stick tiles.
You could use tin squares or have glass or plexiglass cut to size. Have holes drilled into the glass. You can paint the wall behind the glass a decorative color and then screw the glass to protect the paint. You could do the same thing by stenciling the wall and putting the glass over it to protect your stencil.
stencils, paint and a clear cote