Bethesda has released a handful of game soundtracks on Apple's iTunes Store, the publisher revealed on the Bethesda Blog.
Soundtracks (with appropriate links) include:
Excellent, but it's best for one to have a US iTunes account if you want to buy them this way, since the AU iTunes Store's prices are undoubtedly higher (e.g. $29.99 AUD for Skyrim's soundtrack).
Otherwise, remember that you can also get the physical 4 CD version of Skyrim's soundtrack, or 320kbps MP3 versions of Morrowind's and Oblivion's soundtracks (at the US prices listed above) here.