ZM-NB47J is pretty decent in my experience, if the chipset isn't overly hot. The mounting system isn't the easiest (small screws (grrrr) and final adjustments are a pain) but it works. If your chipset really gets toasty (if you overclock like crazy for example), I don't think it's your best bet. The best chipset cooler I've played with is the Thermalright HR-05 IFX. It performs great with little airflow and it fits an 80mm fan if you really want major cooling. The mounting system is a little better, but you need to remove the motherboard. .
I agree with frenchie. Having used both the ZM-NB47J and the HR-05 IFX myself, go for the HR-05 for the NB. I've used the NB47J on a SB instead (it fits!) but without some airflow it can get a little hot. I imagine using it on a NB with an IGP it would get hotter still.