Xenocraft is a texture pack that transforms Minecraft into an alien planet. Almost every texture has been changed or recolored (and I'm planning to change the recolors into new textures in the future), and the pack is designed to follow Minecraft's aesthetic while still seeming alien. There's actually a bit of backstory hidden in it; see if you can find it while playing!
SCREENSHOTS:
http://www.minecraftforum.net/topic/1543527-wip-151-paleocraft-realistic-dinosaurs-in-minecraft/#entry18859975
http://www.minecraftforum.net/topic/1543527-wip-151-paleocraft-realistic-dinosaurs-in-minecraft/#entry18859975