I’ve recently come across the open source software Xplanet, which will render images of the globe with very realistic results.
I render them in 512×256, 1024×512, 2048×1024 and 4096×2048 resolutions. The clouds information is obtained from weather satellites and is typically around three hours old.
I also use monthly map files so that the snow/ice on the planet is more realistic.
Check out my real time renders at /earth/.