Two important questions - how much light will this thing get, and how long do you want it to be able to be left more or less alone before requiring radical work (major cutting-back or removal of some plants or total replanting)? (Small auxiliary question #3: what temperature will this be at - warm room temperature, or getting cool at night?)
If you could give some hint about those things we could probably make better recommendations. But, as a "generic" answer, some usually-all-purpose easy-to-find small terrarium plants would include small ferns, selaginella, creeping fig, creeping charlie (if you cut it back frequently!), baby's tears (ditto, and best in fairly bright light), and my all time favorite small terrarium plant Fittonia (I prefer the white-veined one, but it comes in pink too). For a larger plant in a small terrarium, consider prayer plant, small rex begonias, cryptanthus, spiderplant, smaller philodendrons, or a young specimen of the Chamaedorea (sp?) palm. Pepperomias make good terrarium plants too IF you have really really well-draining medium, but will rot if they get soggy feet.
There are a number of other plants often used in terrariums (swedish ivy, dracaena, croton, larger ferns, larger palms, etc) BUT they will fairly quickly outgrow a 10g tank.
(e.t.a. - I should also mention one of my other all-time favorite sort-of-terrarium plants, the jewel orchid, whose latin name used to be Haemaria but I kind of think it may have changed, anyhow it has gorgeous burgundy-ish pinstriped velvety-looking leaves. Flowers are ok but it is basically a foliage plant. It does quite well in very bright indirect light in an open-topped fishtank, so you have somewhat elevated humidity but not stagnant air. If you are considering an open-topped terrarium, this makes an awfully nice centerpiece )
If you have a Home Improvement Store, there is a good chance they have one of those stands with a load of various houseplants in small 2 inch pots. Any or all of these will thrive in your terrarium. They will likely fill up, but they also will dwarf because of the restriction in soil.
Get creative! Just have fun! What ever shows up to be a monster just pull them out and pot them up! Terrariums are meant to be cultivated and nurtured just as a mini garden would be. Just experiment.
You might include an African Violet or two!
Once you get one going you might consider adding a frog or two!
Anyone that sells frogs in a pet store can help you choose the right plants and the right settings!
One time, a few seasons back, I was watering the roses and suddenly out of nowhere I hear this voice!
"Ronnnnn", in a deep voice! "Ronnnn"
Well, I gotta tell ya, I don't often get company but I turned and looked this way and then that way but no one was there. I was thinking maybe I was hearing things.
Suddenly, again "Ronnnnnnnn"!!!!! This time with more emphasis!
So I said "What?" "Who is that?", loudly across the yard.
and then it happened again, "Ronnn" and out jumped a big old toad from beneath the roses!
I literally stood there in shock! LOL It was the frog calling for his girlfriend not me! LOL