For those that wish to move beyond the medieval realm of vanilla Minecraft! Take note, many of these texture packs change how the Minecraft world looks considerably, it's very easy to get confused.
I would recommend using these only for single player, creative worlds, or as a fundamental server requirement to avoid potential misunderstandings. Some of the texture packs will recommend additional mods to download, so be sure to follow their instructions.
If you're as old as I am, you remember the days spending hours playing games on your brick Gameboy earning neck cramps and replacing the 4 AA batteries that it required. This texture pack takes you way back.. It doesn't just have the same green monochrome color theme, but the blocks themselves have that classic Nintendo art style.
Download here.
Have you ever wanted to go to the moon? Eat cheese on the moon? Dream of electric sheep? A very old pack that I am happy to see still around and updated. The_Fool76 also has 3 other texture packs to take a look at, which you will see in the link provided.
Download here.
A drastic change from regular Minecraft, many blocks look nothing like what they were originally. It's absolutely perfect for building a futuristic science lab.
Download here.
Another sci-fi pack, only this one takes you to a strange alien world. Very futuristic, and creative.
Download here.
Enrich your Minecraft experience! There are limitless opportunities for experiments and testing, enough for someone to make a working Portal Gun mod go with this.
Download here.
Another post-apocalyptic world only more depressing. All hope is lost and all that's left are the ashy, and sometimes mutated, remains of the past. Started by the famous Doku and has been continued by fans.
Download here.
Who doesn't love a good post-apocalyptic world? The pixel art is as lovely as abandoned your world feels. Maybe single player Minecraft isn't so bad after all?
Download here.
Sometimes, a cookie is enough sugar. Sometimes it's not and you want to go full-on diabetic. High on Sugar turns Minecraft into an adorably girly candy land. A wonderfully sweet work of art that also includes support for Random Mobs.
Download here.
The first of two steampunk themed texture packs. The level of detail is enjoyable and many of the blocks are animated. It gives you a interestingly scary steampunk atmosphere.
Download here.
The best for last, Glimmar's Steampunk has a ridiculous amount of textures to customize the texture pack to your own needs. The level of detail blows the mind, it doesn't look it but it really is just 32x32 in size. I can't write enough to say how outstanding this texture pack is, so you'll have to see it for yourself.
Download here.