(Happy Valentine's Day, if applicable.)
This is an odd category to build a list around, because "terrariums," actually, is sort of hard to define. I usually assume, when I hear "terrarium," that we're talking about an enclosed glass container, no bigger than a couple feet in any direction, that's being used to grow moisture-loving plants, but of course there are also extremely large terrariums, terrariums that fit inside an incandescent light bulb, open-topped terrariums, desert terrariums, unplanted terrariums which house animals, etc.
So if you want to get technical about it, there's no plant that couldn't be grown in some kind of terrarium if one is sufficiently flexible about the definition, so the list of "plants for terrariums" equals every plant that exists. Which is an easy answer, but not particularly satisfying.
So what I'm assuming with this list is that we're talking about: an enclosed glass container, no bigger than a couple feet in any direction, that's being used to grow moisture-loving plants. Which means that we're looking for plants that like humidity and moist soil, which grow slowly, and don't need full sun. (Full sun is fine, except that it also comes with quite a bit of heat, and since there's nowhere for heat to escape in an enclosed terrarium, sooner or later an enclosed terrarium in full sun will cook itself to death.)
Which is still a pretty long list, it turns out.
Cryptanthus NOID. Some varieties can get to be pretty large, but most of the ones I've seen top out at about six inches across (15 cm), and they don't spread like some of the choices on this list will.
Episcia 'Coco.' Happy Episcias will produce plantlets on runners, which should root when they contact the soil (you may need to pin them down gently first, so they're firmly in contact), so they do spread a little, but they stay short.
Fittonia albibenis cvv. are fast-growing, spreading plants. The small-leaved varieties stay very short, while the varieties with larger leaves reach about six inches (15 cm) tall and then bend over under their own weight. The stems root when they touch soil, so over time they'll expand.
Hemigraphis exotica. Can get to be twelve inches (30 cm) tall in good conditions, though usually they're shorter than that.
Hemionitis arifolia. Also to about 12 in / 30 cm tall and about as wide. Mature plants will produce plantlets where the petiole joins the leaf; I'm not sure if they'll bend over and root on their own, or if they have to be helped, but either way, allow a lot of space.
Pellionia pulchra. Fast-growing, aggressive trailing plant in a terrarium. Stays short, but the stems need to be cut back periodically.
Peperomia argyreia. Another somewhat mounding plant that needs about 12 in / 30 cm in height and diameter.
Saintpaulia 'Harmony's Red Star.' I don't know about this variety specifically, but there are many, many Saintpaulia varieties, including miniatures (under 6 in / 15 cm in diameter). (Most get to be larger.) All grow well in terrarium culture, and stay relatively short. Spent flowers do need to be removed regularly, so this may not be the plant for you if you want to plant your terrarium in a narrow-necked bottle.
Soleirolia soleirolii, chartreuse cv. This is another low, mat-forming ground cover. Plants stay short but will spread fairly quickly if not cut back.
Recommends and anti-recommends are more or less pointless here, because what's going to work for you depends on the size of terrarium in question and what you want it to do. If you're interested in planting a terrarium, find out how big the plants you're thinking about including will get before you plant them. You should also try to find out how fast they'll grow: some people like having to get in and prune back the plants every so often, and some people don't.
A few of these plants will also need a more specialized growing medium than ordinary bagged potting mix. Most orchids would like the conditions in a terrarium just fine, but need to be planted in bark instead of potting mix, so I left them off the list.
- Adiantum capillus-veneris (maidenhair fern)
- Aeschynanthus spp. (lipstick plants, goldfish plants)
- Asplenium antiquum (birds-nest fern)
- Asplenium 'Austral Gem'
- Asplenium nidus (birds-nest fern)
- Begonia rex-cultorum cvv. and small rhizomatous Begonias. I personally wouldn't try to grow a rex begonia outside of a terrarium.
- Blechnum brasiliense (tree fern) and other tree ferns
- Most Calathea spp. are suitable, at least when younger
- Chamaedorea elegans (parlor palm)
- Codiaeum variegatum cvv.
- Columnea cvv.
- Cryptbergia cvv.
- Cyanotis kewensis (teddy bear vine)
- Cyrtomium falcatum (holly fern)
- Davallia spp. (rabbit's-foot fern)
- Didymochlaena truncatula (mahogany fern)
- Dionaea muscipula (venus flytrap), though they have fairly specific temperature and water-quality needs which won't necessarily mesh with other plant species
- Epipremnum aureum (pothos)
- Ficus pumila (creeping fig)
- Some of the smaller Guzmania cvv.
- Hypoestes phyllostachya (polka-dot plant)
- Ludisia discolor (jewel orchid) and the other jewel orchids like Macodes and Goodyera spp.
- Maranta leuconeura cvv. (prayer plant)
- Nematanthus cvv. (guppy plant)
- Some of the smaller Neoregelia cvv.
- Nephrolepis exaltata cvv. (Boston fern)
- Pellaea rotundifolia (button fern)
- Peperomia caperata
- Peperomia clusiifolia
- Peperomia glabella
- Peperomia griseo-argentea
- Peperomia obtusifolia cvv. (baby rubber plant)
- Peperomia orba
- Peperomia verschaffeltii
- Some self-heading Philodendron hybrids, especially 'Autumn,' 'Moonlight,' and 'Prince of Orange'
- Philodendron brandtianum
- Philodendron hederaceum cvv. (heart-leaf philodendron)
- Pilea cadierei (aluminum plant)
- Pilea depressa (baby toes)
- Pilea involucrata cvv. (friendship plant)
- Pilea microphylla
- Pilea mollis 'Moon Valley'
- Pilea nummularifolia
- Pilea peperomioides? (Chinese money plant, missionary plant)
- Plectranthus oertendahlii?
- Podocarpus macrophyllus (Buddhist pine)
- Polypodium formosanum
- Polypodium grandiceps (elkhorn fern)
- Polyscias fruticosa cvv. (ming aralia, parsley aralia)
- Pteris cretica cvv. (table fern, Cretan brake)
- Saxifraga stolonifera (strawberry begonia)
- It seems to me like Schlumbergera cvv. (Christmas cactus, holiday cactus) ought to work, though I can't say I've seen it attempted much.
- Scindapsus pictus (silver pothos)
- Scyphularia pycnocarpa (possum tail fern)
- Selaginella spp. (spikemoss)
- Miniature Sinningia cvv. (gloxinia)
- Smaller Spathiphyllum cvv. (peace lily)
- Streptocapus saxorum (streptocarpella)
- Streptocarpus cvv. (cape primrose)
- Stromanthe spp.
- Syngonium podophyllum (arrowhead vine)
- Syngonium wendlandii
- Tillandsia cyanea and other Tillandsia spp. (pink quill, air plants)
- Tolmiea menziesii (piggyback plant)
- Tradescantia spathacea? (moses in the cradle, oyster plant)
- Vanilla planifolia? (vanilla orchid)
- Small Vriesea cvv.