Rainbows are shoaling fish in a loose kind of way and are better kept as larger groups of maybe one or two species. The neon dwarf are beautiful fish and I would definitely recommend a nice shoal of them, you should also try to get a mixture of males and females so that the males show their best colours, the females are smaller and not as colourful but they show of the males to the best advantage. I think u could then also get a small shoal of some of the bigber rainbows, like the Red's or Boesmanni's again a mixture of males to females, but remember these grow quite large so dont overstock. Here in the UK I recently saw dwarf neons on sale for £4.00 but I have seen them cheaper and didnt buy them as I thought that was too dear. Red Rainbows here always cost £5.00 for a good sized juvenile fish. Recently my lfs had Macculoch rainbows they were very nice fish and dont grow quite as big, I would definitely recomend them if u ever see them though I think they are quite rare. Hope this helps