I'd suggest something along these lines;
For the top, marbled hatchetfish (Not the brightest of colours, but their unusual body shape makes up for that) or male guppies for the colour, or gouramis; pearl gouramis are nice, have pretty markings and the males get a lovely red throat when they're in breeding condition.
For the middle, one large, or two smaller shoals of barbs or tetras (but avoid tiger barbs, unles you don't want anything else!).Rummy noses have interesting colour and markings, five banded barbs are nice, red phantoms also are an interesting shape.
For the bottom, corydoras catfish or loaches (zebras are lovely; they look almost like thay've been woodgrained, but avoid clown loaches, as they get too big for your tank), if you have sand rather than gravel, and/or bristlenoses, which are ok on gravel and kids love the 'uglies', IME. Or you could have Bolivian rams or apistogrammas, which are very interesting characters.
There's a few suggestions to start you off anyway
