I have a 20 extra tall, I have 2 gourami's, 2 dojo loaches, and 8 head and tail light tetras in now. I'm running an emperor 280 on it. It's right next to the dining table, and everyone loves it. I have to keep my "pretty" fish in the dining/living area. My fish that eat other fish are in my room....lol.
With those tall tanks, I've found that if you put in your bottom fish, your surface fish, and some mid water dithers, it comes out really nice, because there's movement in the whole tank.