I have kept a few rainbow species in my planted tanks. I have DIY CO2, though I haven't tested the dKH in a while. I currently keep Melanotaenia pierucciae, but in the past I have had M. herbertaxelrodi, M. lacustris, and M. trifasciata 'Goyder River'.
I think the coolest thing about planted tanks and rainbowfish is the surprises you get from time to time. Most of the Melanotaeniids will spawn in bushy plants, and once in a while an egg or two will grow to adulthood.
I used to keep Pseudomugil gertrudae, but they're just too small to really appreciate in anything larger than a 10 gallon. I feel the same about most of the blue-eyes.
Here are a few species of rainbowfish that are particularly spectacular, if you can find them: Glossolepis pseudoincisus, G. sp. 'Zig-zag', Melanotaenia catherinae, M. duboulayi, M. trifasciata 'Snake Creek', and M. affinis 'North New Guinea Blue'.