Yea not going to be salt. To much of a pain for salt at work. I like the idea of shrimp and different tetras.
Male and a couple of female, bettas!
id go the red cherry shrimp route, they'd feed on algae etc over the weekend; and are surprisingly enjoyable and active in small desktop tanks such as the one you mention.
Another variable is the bioload, with cherries you'll be changing water not as often as you would with a betta say. Means less hassle in work etc
Dwarf cichlids.