2048pixels. Sadly 20480pixels doesn’t support the Retina MacBook Pro family’s 2560 x 1600 or 2880 x 1880 resolutions, but it’s probably the go-to site for the third-gen iPad (2048 x 1536).
Before you download one of 2048pixels’ wallpapers, be sure to fiddle with the “FX” button in each image’s upper-left-hand corner, where you can actually custom-tailor the properties like blurring, textures (lines, mesh grains) and pixelation.
Cost: free.
Federico Sironi / 2048pixels
Matthias / 2048pixels