At first I thought about some boraras species, but then these might be too colourful for you already colourful tank. You want something to stand out which doesn't take too much attention away from the scape. So, maybe a bit more subdued. How big was your tank again? What about a shoal of neon rainbow fish? Or something whitish, can't think of a white shoaling fish at the moment, but I think the rainbow fish would be great.
Edit: what about smaller barbs? Such as the eight banded false barb?