Windows: Earlier this week we highlighted how to download National Geographic's stunning desktop wallpapers in one fell swoop. That method required some command-line work and didn't grab 2007 images; NatGeo Wallpaper Downloader snags every 2007, 2008 and 2009 wallpaper with point-and-click ease.
Just download the app, point it toward the folder you want to download those wallpapers to, and let 'er rip. NatGeo Wallpaper Downloader is entirely portable, so you don't need to install anything to use it and you can easily pop it on your thumb drive to give the gift of awesome wallpapers everywhere you go.
NatGeo Wallpaper Downloader is a free Windows download. If you're on Linux or OS X, the previously mentioned method should get you there (minus the 2007 images) with a little more legwork.