Hi Sally,
Thanks for contacting Ask an Expert.
There are many leafy plants that are well suited for terrariums. Among them are:

1. Watermelon Peperomia.
2. Starfish Plant.
3. Polka Dot Plant.
4. Pollyanna Vine.
5. Silver Nerve Plant.
6. Pothos.
7. Creeping Fig.
8. Croton.
9. Friendship Plant.
10. Spiderwort.

However, you need to know that almost all plants will outgrow the terrarium.
You can also go with succulents in the stone crop family most are low growing or training. they include sedums - many varieties.  Many of the garden shops around have newer or different varieties from the big box stores. They are usually very easy to take out of the pot and put into the terrarium.
One thing to remember is they don't like wet roots. Water sparingly if you intend to keep it in a non-draining container. Here are some other succulents:
Burros Tail, Crown of Thorns, Jade Plant, Panda Plant (fuzzy), Roseum (pinkish tinge), Zebra Plant, Hen and Chicks (they come in all sorts of colors now including a ruby red, lavender gray, maroon, and on. Then there is Zwartkop and one call Sunburst, really different with yellow and white stripes.
That should give you a start.  
Here's an article from Oregon State on starting a terrarium. Have fun with your new project. Hi Sally,
Thanks for contacting Ask an Expert.
There are many leafy plants that are well suited for terrariums. Among them are:

1. Watermelon Peperomia.
2. Starfish Plant.
3. Polka Dot Plant.
4. Pollyanna Vine.
5. Silver Nerve Plant.
6. Pothos.
7. Creeping Fig.
8. Croton.
9. Friendship Plant.
10. Spiderwort.

However, you need to know that almost all plants will outgrow the terrarium.
You can also go with succulents in the stone crop family most are low growing or training. they include sedums - many varieties.  Many of the garden shops around have newer or different varieties from the big box stores. They are usually very easy to take out of the pot and put into the terrarium.
One thing to remember is they don't like wet roots. Water sparingly if you intend to keep it in a non-draining container. Here are some other succulents:
Burros Tail, Crown of Thorns, Jade Plant, Panda Plant (fuzzy), Roseum (pinkish tinge), Zebra Plant, Hen and Chicks (they come in all sorts of colors now including a ruby red, lavender gray, maroon, and on. Then there is Zwartkop and one call Sunburst, really different with yellow and white stripes.
That should give you a start.  
Have fun with your new project. Here's an article on starting a terrarium from Oregon State:  https://today.oregonstate.edu/news/go-miniature-glass-terrarium
If you have further questions, please contact us again.