You might consider rainbow fish - New Guinea red rainbows and Bosemani Rainbows. They are all very active, colourful fish, like groups, grow to a good size (especially the red rainbows), prefer the upper regions of the tank and are non-aggressive as well as hardy.
giant danios are smaller, but similar. if you don't mind them being aggressive, the halfbeaks are fairly small. oo oo archer fish they're great, but they narrow your choices for tankmates. Gouramies spend a lot of time near the top, but are slow-moving, and can be upset by rowdy fish.
as for middle swimmers - anostomus anostomus (headstander) is a lovely looking fish IMO. medium sized barbs. The up to 6" bracket is a fairly large one for middle swimmers. Have you got anything like a Baensch aquarium atlas? i find them to be like fishy mail-order catalogues