My experience echoes what Jan and others said regarding the versatility of Nepenthes. I now have about half my plants growing in East/South exposure windows, with no terrarium, and after adapting to the conditions (which took a while for some of them), most of them are pitchering and growing, albeit slowly.

The one single most important thing as far as i can tell is... light (and not drying out completely). If you don't supplement the lighting in the dark winter season, the Neps will slow down and stop pitchering. Now that the days are getting longer again, the plants are popping out pitchers all over the place.

Species i am growing on the windowsill (humidity ranging from ~20% to %80 or more):
N. sanguinea (dark red form)
N. ventricosa
N. alata (Luzon)
N. aristolochioides x thorelii
N. rafflesiana
N. ramispina
N. albomarginata
N. fusca / stenophylla
N. truncata (highland)

The first three expect a LOT of light, and do great when outside in full sun over the summer. They just kind of hold on during the winter.

N. ampullaria (spotted)
N. burbidgea
N. adnata
N. sibuyanensis (recently added)

may not do so well. They grow, and sometimes pitcher, but the pitchers are significantly reduced in frequency and size. The adnata is just picky in general. It consistently and slowly grows regardless of what conditions i have it in, but is finicky about pitchering.

Most pitcher seem to last less time in the less humid conditions, too.

I have an N. ampullaria red form in the windowsill as well, but in a large plastic bag, and it is doing pretty well. However, it is getting too wide to fit in the bag. It refuses to produce basal pitchers for me, though, which is annoying since it's now more than a meter tall.