Since Monday, Magic: the Gathering Arcana has started previewing the next big set, Shards of Alara, by showing desktop wallpapers of the five shards. The shards previewed so far are Naya(green), Bant(white), and Esper(blue). Here's a glimpse of these wallpapers. Pretty cool art!
Naya (previewed August 11) Bant (previewed August 12) Esper (previewed August 13)
You can download these wallpapers in the Magic Arcana archive here.