Ásatrú is much in the news these days. So how do you pronounce it?
Well, let me give you the pagan answer: it depends.
Ásatrú = ása, “of the æsir” + trú, “trust, faith, belief.” (Trust, true, and the archaic verb trow—as in I trow, meaning “I trust”—are English cognates of the second element.)
That Ásatrú is both an Old Norse and a Modern Icelandic word tells you a lot about Iceland. The language has changed so little that these days kids in elementary school can still read sagas written 1000 years ago with just a few footnotes per page.
Old Norse Ásatrú: AH-sa-tru. (That's AH as in “Open your mouth and say—.”)
Modern Icelandic Ásatrú: OW-sa-tru. (OW as in “How now, brown cow?”)
So you can take your pick. Me, I learned my Icelandic from the redoubtable Anatoly Lieberman, whose informed opinion was that, Icelandic being a living language, we might as well pronounce it as current speakers do.
For me, it's also a matter of the kind of pagans/heathens that we want to be. Are we a museum exhibit, the ancestors fossilized, or are we the living heathens/pagans of our own day?