Well in that case, let me introduce Desktoppr, a free and online gallery site that collects high quality backgrounds for desktop. The site provides huge collections of wallpapers you can grab. If you register there, you can even upload your own to the public gallery.
But that's not all, one thing that will likely get your interest is this site is Dropbox ready which means you can send your wallpapers from Desktoppr to your Dropbox easily, it takes one single click. To do so, you need to link your Desktop account first to the Desktoppr. Afterward can save the wallpaper to Dropbox.
Interested? You can directly visit Desktoppr site.