I asked this same question in the chat room a when I was seeking Permission. After some degree of debate the yz spelling was generally decided to be correct.

Blasted Tanks. ;-)

I prefer the "z-y" spelling, as that's the original MiB spelling. Doing it the other ways is one of my personal pet peeves...

I'm American. But I think the Men in Black wikipedia page would be the expert on this.
Or you could call it the flashy thing.

I think the term originated with the Men in Black film. The spelling given on its Wikipedia page is "Neuralyzer," so I take that to be the correct spelling.

~Neshomeh

British spelling- Neuralyser
American spelling- Neuralyzer

We are international, yeah. I am not sure if across the pond, they simply do not like the zed, or if over here, we put zees in everything willy nilly.

English is silly. :D

I dunno about the 'i' It's spelled with a y on the wiki. I am not sure if spelling it 'Neuralizer' is less right than 'Neuralyzer.'

I go with the wiki spelling. The instrument in question is spelled 'Neuralyzer' on the Men in Black wikipedia page, but a fair number of sites spell it either way, i or y.