Several anubias species (I love my afzelli) and crypt species look good in the mid-ground IMHO. Any bushy plant can be a pretty mid-ground plant if you're willing to trim it constantly. I think Micranthemum umbrosum (not Hemianthus micranthemoides aka Micranthemum micranthemoides ) is good for mid-ground. Bulb plants are nice too. I love the different aponogeton species.