I hate to be the party-pooper in your terrarium dreams but most terrariums (including the one in your photo) are built for the photo and are not sustainable. Everyone of the plants in that photo are seedlings that will soon outgrow the bowl. And what do you suspose the pond and waterfall are doing? Unless there's a pump hidden in there somewhere, that is gel and its not moving (or even liquid). Sorry! Someone had to say it.
If you want to build a truly sustainable terrarium, choose a good sized tank (at least 20 gallons - Gina's 50 gallon would be better yet), then choose plants that stay small and will do well in a very wet environment: Button Ferns, miniature orchids, sundews, Club Moss (Selaginella). There are a lot of lists of the perfect terrarium plants but, what they have in common is that they only get 12 inches tall... if you only want a couple plants in your terrarium, they are good choices. I don't want to replant every month because my plants have gone crazy.
I love my Streptocarpella but it quickly outgrew its 20 gallon terrarium, mowed down all its room mates and is now outside the terrarium on a humidity tray all by itself. I have a 20 gallon terrarium full of miniature orchids that are going on their 4th year. A couple have been moved out because they just weren't doing well but, otherwise, they are healthy and happy and have not outgrown their home.
It all has to do with planning: ultimate plant size, moisture and light needs, potting medium. Its a community - make sure they can live together.
