I'm going to be getting a new iMac soon, and I was just wondering if anyone has any opinions on what's the best place/brand of memory to buy if I want to upgrade to 16GB. I have a hard time believing that the apple memory is worth $600, but I also think there's differences in quality so I am hoping someone can recommend a quality aftermarket brand.
As the title says, looking for 4x4GB 1333MHz DDR3 SDRAM for a 27" iMac.

-Dave

(a matter of opinion - not everyone will agree with me...)

I treat RAM as a "commodity" - I go to reputable dealers online and buy the cheapest total price (including shipping and taxes, etc).

Suggested dealers:
http://www.macsales.com/
http://www.newegg.com/
http://www.amazon.com/
http://www.18004memory.com/

I've just fitted some 4GB memory from Crucial. Came promptly and works well.

I'm in the UK and used http://www.crucial.co.uk I bought from them before. They were recommended to me by a guy in commercial IT.

But there is another global site http://www.crucial.com

They have a quick scanner that will tell you what you need, if you are unsure.