I really like the Fluval Edge, but I'm thinking of a betta, and that one really wouldn't work in an Edge tank. That biOrb is awesome, but well outside my price range. The other is similar to a lot of brands I've seen, but the back side is completely covered, so it wouldn't really be viewable from both sides.
A 12 gallon long tank might work, if I could figure out a way to "hide" the filter on one short end of it. I'll have to give that some thought.
With the 12 long you could simply put something that grows out of the water in the end with all the gear like say Pothos or other vine/climber then just have it grow along the tank(it can stick to the tank by itself) I use to have a 40 breeder with several starts of different plants that grew from the outside box filters on the back(gave starts to I don't know how many people of those plants). They kept the tank clean of most excess nutrients and I never had a problem with having to clean out the filter box but once a year or so.