Minecraft’s modding community has been around since the inception of the game itself, and remains strong with promised support from the developer, Notch. The world of Minecraft Texture Packs is far too large to be contained in a simple must-have mod list, so it gets it's very own.
Minecraft brings out artists from everywhere. Eldcraft, in particular, is made by a professional video game artist Jonatan Pöljö. Though the world of Minecraft is a world of flat cubes, amazingly Eldpack gives it a 3D look without the use of outside mods. The level of detail within its textures shows a lot of love.
This is by far one of the best texture packs out there; the level of detail is mindblowing and there are nearly 700 variations of textures available for use. Nothing has been forgotten or left behind and it even comes with support for other mods. There's enough clockwork gears in this pack to choke an iron horse. There's even clockwork mobs! To anyone who is a fan of both Minecraft and Steampunk, this is a necessary mod.
A medieval style pack with an RPG flavor, JohnSmith's pack is another well loved Texture Pack. It comes equipped with a customizer, so you can create your own unique version of his pack. It also works with other mods.
Doku's been a long time favorite in the Minecraft community for his texture packs. Starting with Doku's RPG, he's finished up with Doku Craft. His pack comes in three flavors. High, Light and Dark. With a style reminiscent of The Legend of Zelda: A Link to the Past, it's hard to see why you would want to use anything else. It’s also available with mod support. Unfortunately there will be no continued support with this pack so if you fall in love with this pack you will have to keep an eye open for continued fan versions. Thankfully, the community is full of talent and we're likely to see textures in the same style and quality, like what happened with Doku's RPG.