please don't put guppies.
assuming your tank is around 12 x 6 x 7, i would say any
1.peaceful fish(if you want a few).
2.too big(preferably small, maybe Cory Panda?)
3.not nippers(ignore if you don't have betta or guppy)
4.fish that have minimal movements(no tiger barbs please)
IMHO, a pair of blue rams would be nice.