I was considering neons, they too are "glittery" I liked black neons for awhile, but now I don't find them as cute, same with glo lights. When it comes to tetras, I'm really picky :0) for some reason.I have 8 cardinals and 8 neons in my 20 long, as well as a female betta. I love the two combined, they school together and I can tell the subtle differences between them I plan to get more soon, just waiting for Petsmart to have them on sale again.
I would maybe try black neons, glowlight tetras...harlequin rasboras are nice, but get kind of chunky in their old age I've noticed.
I kinda of like harlies, but I'm not "IN LOVE with them" like I am the cardinals now. (sadly 3 died, 2 over night, 1 this morning, water params are good though).
Any fish that aren't tetras that you think would work? I was *considering* rainbow fish? Like turquiose rainbows (Saw them at petsmart as well)
I'll probably just have to go look at fish for awhile, that's how I determine what fish I usually get when I'm not sure