Nepenthes burkei. I remember trying to compare a so-called N. burkei and N. ventricosa without seeing any features that separates them from each other. It was no surprise when I found a pic of what seems to be the real N. burkei.
Here's a link to a Japanese grower's website, which hosts a very nice gallery of plants.
I was wondering to myself that this plant doesn't get much attention (as far as I know). Does anyone actually grow this species in the US or Europe (I wouldn't be surprised if Tony P. does)? I personally find this plant to be one of the most beautiful I've seen so far. I don't know about everyone else, but I think this plant deserves more attention!