A number of online vendors sell FCE for a lot less than the Apple Store. One I looked at had a "Gauranteed Real" stamp over the image of the software, as if there may have been reason to doubt the authenticity of the software.

Of the discounters who knock up to $50 off the price of FCE, who do you guys like?

Check out the sponsors page. They are not only reputable dealers with fair to some of the lowest $ but they also support this site.

If they have to put a "Gauranteed Real" stamp on it, that substantially increases the likelihood that it isn't.

I often buy from B&H.