Clowns, firefish, clown goby (actually, there's a ton of nano sized goby), royal gramma, jawfish...
IMO, you could fit 4 fish max in a 24g, maybe 5 if you do a really good, small set of fish, like 2 clowns, a firefish, royal gramma, and a clown goby.... but clowns get somewhat big, so that might be pushing it.... unless you add a nano sized skimmer.