Neon tetras is prob my most faveroute though there is lods. Its becuase they look fantastic when you have lods of them and they're not that difficult to keep.
I'd have to say Neon tetras....they just add so much color.
And bala sharks...I used to watch them prowl in my tank for hours and for some reason I would hum the Jaws tune...nunna.....nunna.....nunna........nunna..... nunna..nunna..nunna.nunna.nunna....um yea you get the idea!
Rummy nose tetras are neat little fish and the schooling behavior is great to watch. They need soft water to thrive, much like Cardinal Tetras, so I don't even try them.
Harlequin Rasboras are very tight schoolers and are a blast to watch. I have a nice school of glo-lite tetras in with my discus and they are beautiful when they school. When they are happy they really do glow and the color is spectacular.
Harlequin razzies are my favorites. They have shown themselves to be quite long lived and hardy, they are attractive, and very peaceful towards the other species.
I have only been successeful with the neons. The rummy nose are awesome but very frail and am not ready to try them again.
The cories are so much fun to watch when you have a bunch of them with only one or 2 they tend to be boring but in a group they are never boring.