With the glass 18x18x24's, I say get more creative! The best part about them is planting them beautifully. Take a look through FLChams's safe plant list and pick a couple which wouldn't be practical in a typical big screen enclosure. There are a lot of fun, smaller options, some of which can add more color or ground cover. Asparagus fern, maidenhair fern, peperomia sp., pilea sp., small crotons, baby's tears, for example.
Of course, you'll want to make sure to get something big and sturdy for an animal to hang out on, too, so our go-to ficuses and scheffleras are always still good options for centerpieces