Featuring bits of artwork based on Diablo themes, characters, and places, you can now download all kinds of media to enhance your mobile experience. The actual Diablo wallpaper section is a bit shabby right now, but as with any new service, it will develop over time (see it here).
The new site also offers ringtones and wallpapers from the Starcraft and World of Warcraft worlds and Blizzard's Battle.net Mobile Authenticator. Check out the whole site here. Most major carriers are supported, with more to come: