There are many options some would be:
Rainbowfish (lots of colors to choose from)
Loaches- (yo-yo's and Angelicus are my fav's for large tanks)
Angelfish (6)
Tetras (a couple schools of different body shaped ones like cardinals and diamonds)
Cory's
Hatchetfish
Rasbora's
Cherry Barbs
Threadfin Rainbows
Dwarf, Honey, or Pearl gourami's
Bolivian Rams or German Blue Rams
Whiptail cats
African cichlid tank
As suggested you should look up different fish and see what you like, make a list, then narrow it down.