HD Wallpaper is a free iPad App which not only gets you high-resolution wallpaper for free but also makes it easy to preview how it will look on your home screen and when you choose the wallpaper for lock screen. This application collects iPad wallpaper from different sources and displays on your iPad. It also gives you an option to email that picture or save it on your iPad.
Apart from this you can also filter according to categories and find out which wallpapers you had already downloaded. Find it on iTunes by 8 Bit Factory Inc