I bet these could be made w/ some concrete and a homemade mold using old fence planks... I also like the natural look of just using old pallet planks or fence planks laid out in the same manner. garden, untitled, by Maureen Anne on flickr
Peony and Iris border: Neighbors down the street have an old stone wall out by the road. A border of pink peonies and various shades of purple and lilac irises grows in front of it. What a glorious sight it is each year.