Everyone and their mother has cardnials and neons (as probably you know which is why you said no to them in your topic). While they're definitely beautiful fish, at least from my observation they don't school that tightly and aren't super active.
It really depends on what you kind of fish you want and how active they want to be. Everyone likes active fish so with that said I've had black neon tetras and glowlight tetras and they swam near the bottom of the tank and weren't super active. I had good experiences with bloodfin tetras (really beautiful and active tetras that I don't see many people talk about... but they are amazing because they can live 10+ years) and espei rasboros.
I think your best bet is to go to your LFS with an idea of the types of fish you would like and hopefully you'll have a chance to observe them. 50 gallons is large enough to house most rainbow fish as well so I would definitely look at them as well. Someone mentioned threadfin rainbow fish and I've had them and they're really beautiful, swim very fast (be sure to have a tank top on or the water not super high as they can jump)... they do have very small mouths so you would have to really crumple up the flake food for them; they could also eat daphnia and bloodworms.