If the Old Norse gods had to choose a favorite food at those legendary feasts in Valhalla, my bet is that it was something like skyr, produced in Iceland from the days of the original settlement in the 9th century. Probably one of the healthiest "yogurts" out there (it's made from non-fat milk , is rich in probiotics, and is so concentrated it contains three times the protein of typical American yogurts), skyr has only been available to buy in America since 2007, when Siggi Hilmarsson introduced it (branded as "Siggi's Icelandic-Style Yogurt" to select stores like Whole Foods and The Fresh Market). I probably appalled the other shoppers (or at least my husband), with the scream of delight I emitted when I found that it had also become recently available here in the Pacific Northwest at the Haggen's chain. However ... until Siggi and I can persuade Americans everywhere to demand access to his wonderful product (my full review is here), this stuff is expensive ($2.79 for a 5.5-ounce container, which make my frugal Norwegian-American blood freeze in horror).
However ... if you have access to a single container of Siggi's plain or vanilla skyr, liquid rennet, and non-fat milk, it's dead easy to make this nectar of the gods at home. Here is both the basic recipe and an illustrated step-by-step skyr making lesson.
Icelandic Skyr image and copy; 5/30/2012 Kari Diehl, licensed to About.com.