Shadowbox for KittyCatS 2D Modes
Bookcase Shelves for KittyCatS Boxes 3D Modes
These are 1-Prim Mesh models sold copy, modify. Actually, they're half a prim: link two together and they still cost one prim.
I set them up so that, if you drop a wood texture on them, the grain runs properly. At worst, all you need do is rotate 90.
The models have 5 faces, allowing you to re-decorate them to match your store's decor.
They are have multiple levels of detail which degrade gracefully. Of course, to see that, you'll have to zoom all they way in, and look at them from very far away. Since that rarely happens, you'll probably be hard pressed to see the detail changes.