Along with the new operating system, Mountain Lion, Apple is also bringing a new wallpaper to make your screen look much better. You must know the fact there is actually 43 wallpapers that Apple chose to hide from you, including National Geographic, the universe, aerial, natural four major categories. Each of these wallpapers come in a 3200×2000 resolution.
OS X 10.8 users can Command + Shift + G shortcut keys to open the Go To Folder from the Finder, and enter the following path exactly:
/System/Library/Frameworks/ScreenSaver.Framework/Versions/A/Resources/Default Collections/
If you wanted to get that new wallpapers in complete high resolution, then you can download it from the link below.
Aerial
Cosmos
NatGeo