I vote for a large school of danios: hardy, always active, color up nice, and school. Either Zebras or a mixed school of zebra, leopard and pearl danios. Physically very similar but the different colors and patterns will give interest and they will school (shoal?) together. Zebras though have always been a favorite since my first tank in the 60's.
If you wanted a cooler tank then White Clouds, under the right conditions their colors pop and they will breed almost as readily as live bearers.