Legendary Pack is an amazing texture pack that changes all of the textures in the game, adding a medieval-fantasy vibe without straying away from the vanilla appearance of the game. The pack introduces custom GUI's, over 100 mob models and entities and completely overhauled biomes. The pack even has custom day/night skies.
Take a look at the screenshots to see what you can expect from this pack. Download links are given below. Read the installation instructions carefully.
How to install
1) Download the texture pack.
2) Most texture packs require Optifine, so make sure to install it.
3) Put the texture pack in .minecraft/resourcepacks folder.