memory upgrade for iMac-NEW4.0GHz QC i7 Turboboost 4.4GHz what do I buy?

If it is a 27", then I'd go to OWC or Crucial - those are the two most recommended RAM vendors for Macs - make sure you pick your model from this page:

http://eshop.macsales.com/shop/apple/memory/iMac

They also have great install videos or here are Apple's instructions:

iMac: How to remove or install memory - Apple Support

+ 1 on the babowa recommendation. Take the advice, it's spot on!

You're welcome!