4-5 male guppies
or
6-8 neon/black neon OR (not and) glowlight tetras
or
4 platies
or
2 swordtails
or
(only if heavily planted first) 3-5 female bettas
or
5 harliquen rasboras
or
4 tiger barbs
or 5-6 cherry barbs
thats for species tanks.. if you want a mix, I personaly like platies and cories.
3 platies and 3 cories
or
4 neons tetras and 4 glowlight tetras

try to stay at or under 1 gallon of water per 1 inch of adult fish. and read about their temperments first