With the fish you have listed and the size of your tank you could do a pair of pearl gourami's or a pair of angelfish. Angelfish aren't nippy but they do fuss between themselves, they are cichlids and that is what cichlids do. Danio's can actually be too zippy/active for angels tho. Rainbowfish are probably your best choice with the fish you have. But how many fish do you have, you only listed what kind. Depending on how many fish you already have you may not even have room for more fish.