Rainbow Fish?
 

How many rainbow fish can i put in a 37 gallon tank?
thanks in advance

You'll have to get smaller ones, look up rainbows @ liveaquaria.com, look for dwarf or at least the small ones. furcatas, hold on, go to www.azgardens.com they have a few small ones to read up on.Also carry"hard to finds" your welcome.
OMG i almost forgot, do not let someone talk you into buenos aries, theyre straight up mean.

Not much for a 37 gal. You could get dwarfs, like catfishtabbi said, but its very unllikely you'd find them. More commmonly, you'd find the bossemani or banded rainbows. For thoses guys, probably only 3 would fit in a 37, at most. They really are schooling fish and anything below 3 would not be good. I suggest you go find those dwarfs, or check out other possibilities. Gouramis are quite similar, especially pearl gouramis, but thats just my suggestion

I've kept and breed boeseamis before and I would have to say the minimum tank I would keep them in is a 4 foot. Mine got 4" long and they are really active fish. I got rid of them because they seemed cramped in my 55gal. They need lots of swimming space. All rainbows do IMO.