Random plant tips: I keep planted terrariums, but with my memory I can never remember exact names of plant species, so I can't recommend anything specific. However, the way that I arrived at the plants I use was to buy really cheap, indoor plants sold at bulk stores (lowes, wal-mart etc.) (1) if there is a massive tray of small pots of plant x at $2.00 a pot, it's probably hearty. (2) if it's an indoor-only plant, particularly if it "looks kinda tropical," it can probably survive the heat & humidity of a terrarium. (3) if it's a $2.00 plant, I won't feel too bad if it doesn't make it. If you really want to get into it, bromelaids and certain orchids can do well in a terrarium, but they require more specific maintenance and conditions, so I'd start with the "bulk-cheap-plants" before exploring more expensive options. (I do have a lady's slipper orchid tucked into my treefrog enclosure, but the humidity's a little too high for it, so I might have to give up and take it out, as it's not blooming.)

Random things to keep in mind for planted terrariums: (1) I've noticed that thicker, deeper green leaves indicate plants that love high humidity. I'm sure this is not a solid rule to live by, but it's done me well. (2) fuzzy leaves tend not to like humidity as much. I used to know the exact reason... the "fur" helps w/ water retention amid native environments that are dry? (Don't quote me on that. It's been over a decade since I took plant morphology.) (3) consider a base layer of activated charcoal underneath your soil to adsorb odor. (4) always keep your pets' comfort in mind. (Some part of me would love to decorate my leopard gecko tank w/ plants, but it's too arid for anything but cacti, and that's not really safe.) (5) As John said, you will eventually have to break it all down to clean and change the dirt, so it'll be a little more work.

I hope some of this helped your planting ideas. I know I always get excited about planting my tanks.