Go with an Asian Cyprinid style tank. They are peaceful and active, and you can have alot of options.
Schools of Bala Sharks, Tiger Barbs, Rosey Barbs, and Clown Barbs (20 of each, atleast.)
Add a few Blue, Gold, Opaline, Platinum, Pearl and any other Gourami's you can find, just not large ones.
Do a school of laid-back catfish on the bottom.. Although not from Asia, a school of Brochis (Emerald Green Corys) would be nice, as they get large but are still peaceful and have little bio-load. Clown Loaches, although expensive, would be very impressive in that tank with a school of 20+..
These fish all get a reasonable size, active, and colorful. They will all eat flakes easily, and are low maintenace. These are the types of fish I see used VERY OFTEN for doctor-office accounts of a friend. If you look around, you can find a number of other good 'Barbs' that have good color and easy maintenance.