Some kind of cichlid or gourami would probably be your best bet.
In terms of cichlids, the various dwarf New Worlds, kribs/pulcher and keyhole cichlids are all common favourites. You can get hold of some quite rare or beautiful ones if you take the time. The only thing to keep in mind is that some will chase your cories around when it comes to breeding and some may pose a threat to your shrimp and/or dwarf frogs. Also, being mainly bottom-dwelling fish, they might clash with your current stocking but they'll appreciate the planting very much indeed.
When it comes to cichlid species, I'm not especialy equipped to make good suggestions but I can give you some gourami ideas if you are interested.
The first that always comes to mind is, of course, the pearl gourami (Trichogaster leeri) as it's my favourite fish. A trio would be nice but I'd actualy suggest a larger group - maybe 5 or so - with a couple of males and several females. Pearls are unusual in that they'll display behaviour very similar to schooling and can be very social. In a large tank, with lots of their own kind, they'll remain very agreeable and peaceful fish. By keeping both males and females, you also encourage the fish to show their best coloring - and they realy are amazing fish when mature. The only issue with pearls is that they
can get nipped but it's rare that they'll be severely affected and a larger group is even less at risk. They grow to 4-5" (males being at the upper end of that) and can easily be sexed as the males develop a lovely deep red-orange ventral color, olive flanks and dorsal area and have an elongated dorsal and anal fin - both of which also posess extended fin rays. Females are plumper and less brightly colored but also have some subtle olive and pink shading.
A fish that might suit you better is the moonlight gourami (Trichogaster microlepis). The downside is that it's not quite as bright and grows larger (about 7"). Having said that, they are almost as peaceful and a single fish would be just as suited to your tank as a trio would (whereas pearls do better in groups). Though they appear a uniform silver, in the right lighting, they have a stunning purple tinge. When males are mature and in breeding condition, their ventral fins turn the same deep red-orange as the pearls' ventral area. The contrast with the purple is beautiful. Females have yellow ventrals (as do males when not in breeding condition). These are harder to sex than pearls but sexing does often seem to matter less with moonlights anyway.
Another fish that would realy suit your tank is the banded (or indian/striped) gourami. The sceintific name is Colisa fasciata and I reccomend you learn that if you are looking for them as they are often mis-labelled (though you realy can't mistake them!). Males are brighter than females and grow slightly larger. They max. out at around 4". These fish look like slightly elongated and enlarged dwarf gouramies but, IMO anyway, have a much friendlier 'personality' and are less likely to dispute territory and cause trouble. Their colors are amazing and even the fish at your LFS should be striking (and they improve as they settle in and mature). The other huge plus is that they, like the moonlights, are unlikely to be bullied by nippers and, like both the afformentioned species, they are hardy and tolerant of a wide range of conditions. A trio would be great but more would work just as well. Also, you can keep several males quite easily without any trouble - but always avoid keeping gouramies in a pair (regardless of sex realy).
Simialrly, I'd suggest the thick-lipped gourami as an alternative to the banded. Colisa labiosa, however, is not usualy as brightly colored (though there are a handful of color morphs to choose between) and they stay smaller - at only 3.5". Again, a trio (or more) is best and they are very similar to the bandeds with respect to behaviour.
There are many smaller gouramies that would work as well but they are not 'centerpiece' material per say. All gouramies will appreciate a planted environment to an extent. The above, especialy, thrive in heavily planted tanks and would realy appreciate them. Contrary to what you might think, once settled in, they are quite active fish (especialy when kept in groups) and heavy planting encourages them to come out and be comfortable. Another big advantage of these large top-dwelling species is that, with your somewhat bottom-heavy current stocking, they'll be filling in a gap in the water column and hopefuly won't be competing much for space with your existing fish.
Other than cichlids and gouramies, have you considered rainbowfish? Even some of the smaller ones (like dwarf neon/blues - Melanotaenia praecox), though they are schooling fish, can finish off a tank very nicely even though they aren't quite on par with angelfish
The larger ones (my favourites are boesmani rainbows and Melanotaenia lacustris) can be even more impressive but I wouldn't feel confident keeping them with your cherry shrimp
Keep in mind that LFS rainbows never look like they will ocne settled in a stable aquarium environment so don't underestimate their beauty - they are called 'rainbow-fish' for good reason.
