Just released my first Skybox pack to the Asset Store. It contains twelve skyboxes, three sunsets, 1 desert, 6 mid morning / afternoon, 1 alien world with cyclone clouds and 1 night. Five of the Skyboxes also form a sequence where the sun is at elevations 2, 45, 90, 135 and 178 with small cloud movements.
Each texture rendered at 2048 x 2048 TIFF and set in Unity by default to 1024 x 1024 PNG (you can change the texture value in Editor to up the quality to 2048 ).
Each Skybox also has a prepared material with all textures applied.
The package has been updated to include six HDR panoramic renders at 4K resolution in .Exr format for Unity 5. A material for each has already been prepared, just drop it into the Lighting tab’s Skybox area.