Some sites that offer free downloadable nature wallpaper include NatureWallpaper.net and WallpapersWide. Each site offers a large selection of nature wallpapers in a wide range of resolutions.
NatureWallpaper.net features nature wallpapers in a variety of categories, including animals, flowers, rainbows, reptiles and African wildlife. The site allows users to rate wallpapers, and it offers the ability to search by keyword.
WallpapersWide offers a nature section with thousands of free wallpapers available for download. The site offers a number of nature subcategories, including beaches, deserts, flowers, forests, lakes, mountains and rivers. WallpapersWide offers many of its wallpapers in HD format, and the site allows users to filter results based on image resolution or aspect ratio.