some seahorses would look pretty sexy in that tank...

I'd second a seahorse tank.

IMHO the peacock mantis is too large for this sized tank. I had mine in a 30g (30" long) and it wasn't ideal, the 17g cube has even less length. They grow to about 6" and would need a lot of room to roam. A G. Smithii is a better choice as it's much smaller. The peacock is very prone to shell rot (it got mine, unfortunately :cry:). You can't keep most corals as any decent coral-growing lighting will cause shell rot.

So far, I think I'm leaning mostly towards something like a nice looking display fuge with lots of different macros.

I stumbled on this yesterday though and it may be changing my mind.

http://i.imgur.com/aXn53HLh.jpg

How feasible to you guys think this is? It's pretty amazing. Is that GSP on the ground?