Hi beginnerfishlover,
There are several kinds of fish that are about 1.5 inches.
You could have a small school (6) of neons or serpae tetras.
I have 4 neons and 4 serpae, so I am 2" overstocked in a 10g.
Guppys grow to about 2 inches, but from what I've read here you should have only males or females, as they reproduce rapidly.
Endlers are pretty, I don't know much about them, only what I've read here.
If you go here, there are links on the left that describe different species.
http://www.fishlore.com/
Good Luck with your tank!