I'm a big fan of minifish right now...something along the lines of 20 Corydoras pygmaeus, 20 Carnegiella marthae, 20 Hyphessobrycon amandae, and 20 Paracheirodon simulans, and either a pair of rams or Apistos would look nice in a SA biotope. The same would go for 20 Danio tinwini, 20 Microdevario kubotai, 20 Boraras briggitae, and 20 Yunnanilus sp. 'Rosy', with a pair/trio of wild bettas (I like Betta imbellis) or sparkling gouramis.
For something for people who like "normal" size fish...10 Carnegellia strigata, 10 Corydoras julii(or similar Corydoras), 10 Hemigrammus rhodostomus, and 10 Paracheirodon axelrodi, and a pair of smiling Acaras or a pair of keyhole cichlids would look nice in the same SA biotope. For an asian biotope, 10 Danio dangila (or similar danio, NOT GLOWFISH), 10 Pangio (kuhli) loaches/similarly sized loaches like yo-yo loaches, 10 tiger barbs, and 10 cherry barbs would look nice. So would a more pacific biotope of 10 glass catfish, 20 harlequin rasboras, 10 chain dwarf loaches, and a pair of pearl gouramis.
For larger fish: you could probably do a zebra pleco, a black ghost knife, and an oscar if you make sure to filter really, really well.
I have a lot of fish ideas....