Lemnalia and paralemnalia are cool, S. elegans (Fiji yellow). Not rare but cool, tubipora musica. Lobophytum (devil's hand) species can be cool and there's a blue variety that's pretty nice. Isaurus (snake polyps) species are very cool, kinda ugly, but cool. Hard to find mushrooms would be amplexidiscus (elephant ear) species, these things can get huge and they can also grab smaller fish. The one soft coral everyone thinks is an sps coral, heliopora (blue ridge) is a true octocoral, not rare, but often overlooked. In the 90's I worked at one of the few coral farms in the country and we had tons of soft corals (over 120 species), so soft corals hold a special place for me. A lot of them will look nice under blues, but there are far more that absolutely shine under daylight spectrums. Xenia (especially pulsing varieties) were treated as refugium species because they were so good at soaking up nutrients.