are you just wanting to keeo the american theme? if so pencil fish, small headstanders and ofcourse tetras, i went fir rosys but there is a tetra so suit all needs, congos work well, if you are not bothered about the region then danios, rainbows, bitterlings, barbs even guppies, mollies and olatys can be used dependent on what cichlid, ofcourse there are other dithers but these are the most common your likely to encounter in a lfs.
Well I was lookin at Serpae teta or cherry barb due to the aggressive nature of the tigers but I think a shoal of 8-10 should keep the aggression between them and also will look quite stunning.
Just going to have an RTB, Firemouth and couple of BN plecos in there.