Hi Davina, I don't grow any but there are many miniature pleurothallids in genera like Pleurothallis, Masdevallia, Lepanthes, Stelis, etc. Masd. erinacea is one that I particularly like, maybe someone with experience with it will chime in.
Bulbophyllums: hirundinis, thaiorum, albociliatum, plumatum, alagense, and catenulatum are all small and fairly easy to grow.
Ornithocephalus, Zygostates, and Hintonella are related to Phymatidium and mostly very small plants. Ocps inflexus is a vigorous and showy species, though not as tiny as some (inflorescences on my clone are 12-15 cm, leaves about 5-6 cm long).
Maxillaria sophronitis, Mediocalcar decoratum, Dinema (Encyclia) polybulbon, Dendrobium lichenastrum, Isabelia pulchella, and Angraecum distichum are a few more that I think will do well in a terrarium.
I look forward to seeing what others suggest. There are a lot of good terrarium growers on here who post nice photos, check out the
subforum on that growing style. You might also find good suggestions on
Dendroboard or other terrarium-specific forums.