40 g. Fresh tank

Hello,

I have a 40g. Long fresh water tank in my office. With live plants
and a large substrate (pebble size) everything is looking quite nice.
I currently have a couple of Raphael Cats, 2 otto cats, and 7 rainbows
(3 bosami and 4 aust.)

At first I planned on finishing the tank with a total of 13 rainbows
(of various species) and a small school of tetras. According to my
calculations this wouldn't over stock the tank. But. . .

I think I want something different, but I'm not sure what. Does
anybody have any ideas? I think I want one fish that will stand out
and make people go WOW, but it has to get along with the Rainbows (I'm
very fond of them).

I was thinking a pumpkin seed fish, but I don't know how well that
will work (I'm not sure of their temperament).

Any suggestions?