Possible Species That Derived
One must note that it is very possible that many Nepenthes originated as a hybrid from two or more species. Indeed, it is thought that most of the current flowering plants in the world originated as hybrids. Just because a plant is found to be a hybrid does not eliminate it from being elevated to species rank. If a hybrid is able to sustain a population in which it can reproduce and establish itself, at some point it can be elevated to species rank. This is especially true if the hybrid has replaced both parents in the locations in which it grows. Some hybrids, such as N. xTrichocarpa have an extensive range,but only appears with the parents (ampullaria & gracilis), and it seems the parents are needed to keep the populations. In this case, the hybrid should not be elevated to species rank. But in the case of N. murudensis listed below, populations of this plant have become separated to some degree from the parents, and the plant has established characteristics which it is able to reproduce on its own. These types of hybrids should be seriously considered for species rank.
N. murudensis - When this plant was discovered, it was immediately thought that it was a hybrid between N. reinwardtiana x N. tentaculata. The one problem with this theory was that N. reinwardtiana was not known from the immediate area (the summit of Mt. Murud in Borneo). It has been recently reported that N. reinwardtiana was found in the vicinity. In any case, it appears that N. murudensis is a self reproducing plant, which does not need the constant interjection of the parents to sustain itself. It's characteristics can be reproduced within its own population, and appears to have been stabilized.
N. petiolata - When I initially saw this plant, I immediately thought it was a hybrid between N. truncata and N. alata. After research, I found that N. petiolata does grow in the vicinity of truncata, and that alata is close by. There have also been reports of hybrids between N. petiolata and truncata in the area as well N. petiolata and alata.