Don't want to build your own? No problem, these starter packs should get you started. Note that these textures were rendered at 4000x2000 using Textures for Planets and scaled down with graphics software.
Four terrestrial planets with clouds. Equirectangular sized 2000x1000.
Download Terrestrial Texture Pack
Four gas giant planets. Equirectangular sized 2000x1000.
Download Gas Giant Texture Pack
Four habitable planets (alpine, savannah, swamp, tropical). Equirectangular sized 2000x1000.
Download Habitable Planets Texture Pack
Four inhospitable planets (ice, volcanic, martian, venusian). Equirectangular sized 2000x1000.
Download Inhospitable Planets Texture Pack
Four cloud textures with alpha transparency for layering on worlds. Equirectangular sized 2000x1000.