you have allot of options
1 male beta
4 cory cats
or
1 male beta
10 Ghost shrimp
or
8 neon tetras
or
6 harlequin rasboras
5 serpate tetras
or
6 male guppys
or
5 male platies
they should all be at 74-79 degrees farenhiet
some tips for small tanks;
do not mix betas and guppys
do not house 2 or more male bettas together
do not mix betas and gouramis
do not keep nippy fish like serpate tetras and tiger barbs with bettas, guppys, and fish with long fins
in small tanks do not keep goldfish unless you can clean it alot an can upgrade soon
do not use an undergravel filter
cycle your aquarium before puting fish in it
some fish may look small and cute in the petstore but reserch before you buy!!! (ex. oscar, angel)
in your tank do not buy a plec, pleco or plecostsumus, the get at least a foot long!
get a geavel vaccum and do 2 gallon wwater changes weekly
never! do a 100% water change
get a cover, fish jump!
never put a goldfish in a heated tank
do not rely on advice from petco, petsmart or walmart
enjoy the new tank and good luck!