The thing about both platies and mollies is that they're live-bearers and thus produce a lot of young. If you don't have predators that eat young, like angel fish, you risk getting overrun fairly quickly.

We have cherry barbs in our larger tank at home, and they're good value, though for appearance, I prefer rummy nose tetra, personally. I also like cardinals, which usually swim in schools, offering a nicer image, and bring a lot of colour to the tank.

Zebras are a fairly ubiquitous in tropical tanks, but that shouldn't stop you if you like them. :)