I found these great hanging candleholders at CB2 recently, and the first use I could think of for them was "hanging terrariums"! I had wanted to do this project for quite a while, but had given up on the hope of finding affordable glass vases. These CB2 glass candleholders are a steal at $3.95/each, and can be used for so many purposes (think of clustering them above a dining room table, or hanging them at various heights above your breakfast counter.)
To keep things simple and easy, I used mine to house two small tillandsia, also known as air plants. If you've never heard of tillandsia, they're amazing little plants that don't need soil to survive. Their namesake isn't entirely accurate, as they do need more than air for survival. Soaking them in water (to the point that would mimic the amount of water they would get in a heavy rainstorm) twice a week is necessary. Otherwise, though, they can live almost anywhere and don't need to be planted in anything - you could even hang them from a string!
I think they look perfect housed in tiny terrariums, though.
