Couple of suggestions:
hardwater tank for shelldwelling cichlids. This would be a species tank rather than a community, but they have great little characters, well worth it. Sand and lots of shells, like the escargots you get from delicatessens.
small group of wrestling halfbeaks (1 male+ females)
dwarf puffer species tank - you could probably fit 3-4 in there
community tank with a group of peacock gobies (1 male, 2-3 females) and small school of small tetras in middle
school of 6 hatchet-fish+ school of khuulie loaches
trio of sparkling gouramis+ school of pygmy corydoras
I have a tank this size which I use to breed small unusual livebearers. If Santa were to present me with another one, I would set it up for shelldwellers as a contrast- a little slice of the Tanganyika in my bedroom.