Your temps will have to be no higher than 55-60*f at any time otherwise you should shoot for an intermediate or forgiving lowlander.
First things first, how large of a terrarium do you intend to have? Depth (width from front to back) is as important as height when considering what size plant you can have as leaves/pitchers resting on the glass may occassionally die faster probably due to trapped condensation between the pitcher walls and the glass.
Some of the smallest highland species (which require a drop to the high 50s at night) include: N. inermis, N. lamii, N. dubia, N. aristolochides, N. talangensis, N. jacquelineae and N. argentii (the most expensive Nep available). This list isn't comprehensive, just off the top of my head. These plants are generally "expensive" and considered difficult but if you can keep the temps cool and the humidity in the 80%+ range you might do well, remember they require bright lighting as well as high humidity, not one or the other. This combination can create more "steamy" conditions during the day, if this happens and the terrarium gets warmer than 80*F while the lights are on then you will need to start up a tiny fan inside the terrarium to cool off the plants. Highland nepenthes leaves and soil surface (like most orchids) should never feel warm to the touch, but cool and damp (but not wet).
Good Luck!
