The store has always given prospective buyers the ability to preview individual tracks. While 30 seconds of sound may not be an adequate representation of an entire song, it is at least enough to make sure that the song you're buying is the one that's been stuck in your head for days.
For previewing entire albums, however, AmazonMP3.com has, since its launch, provided a better solution for previewing entire albums. TUAW's own first look at Amazon's would-be iTunes killer in September of 2007 noted the convenience of the site's 'preview all' button versus the need on iTunes to select each track to preview individually.
Why it's taken a bit over two years for iTunes to catch up remains a mystery, but let it. Hit the 'Preview All' button and let the music play (in 30-second increments).
Thanks pisbonanza for the tip!