MOST tiles, when you look at the tile sheets, indeed the majority of everything comes in both facings. For grounds I use decal/splat tiles which can really be used in either or both capacity simultaneously as they have faded edges which allow for them to blend in with other textures. I do have more rigid tiles (in diagonal) in the newer 2.5D asset packs. If you haven't checked it out, you can download the Infernus tileset for free and find those kinds of tiles as well.