The world of Minecraft mods has never been richer. From tech, to magic, to nature, there's so many ways to expand your in-game experience in exciting ways. Below, you'll find what I reckon are the best Minecraft mods available today. Almost all of them require an older version of the game to play—usually version 1.7.1.0, and quite a few also require the Forge modloader or other files. Follow the installation instructions carefully, and you'll be fine.
They're all brilliant on their own, of course, but it's worth noting that they might conflict with each other a bit if you try and install several at once. If you do struggle with that or other issues, consider trying a preconfigured modpack out instead—the launchers provided by Feed the Beast and the Technic Platform are one of the easiest ways to quickly and cleanly get playing modded Minecraft.
Now, without further ado, let's get started.
Optifine
[1.8.1]
Minecraft doesn't scale too well to the power of fast or slow machines. It runs surprisingly poorly on low-end laptops, and a high-end rig can't do much with its extra oomph. Enter Optifine—a mod that not only makes Minecraft run faster but also look far better. It supports HD textures, smooth lighting, and more, and framerate doubling is not uncommon. It's one of the first things I usually add when installing Minecraft. Grab it here.
Twilight Forest
[1.7.10]
Love adventuring? This mod adds a new, densely-forested dimension shrouded in perpetual twilight that hides both valuable treasures and dangerous monsters. Throw a diamond into a pool of water surrounded by flowers to create a portal there, then spend a while roaming around. You'll find hedge mazes, hollow hills, enchanted groves, glaciers, lich towers and more with rich rewards for those that delve the deepest. Grab it here.
Biomes O'Plenty
[1.7.10]
Since the 'Update That Changed The World' in late 2013, there's been a bit more diversity in Minecraft worlds. But Biomes O'Plenty adds vastly more—75 to be exact—from brushland and coral reefs, through lavender fields and ominous woods, to tundra and wasteland. You'll need to create a new world to use it (make sure to select the 'Biomes O'Plenty' world generation option), but it's worth it to see corners of Minecraft that you've never seen before. Grab it here.
Botania
[1.7.10]
Some mods add powerful magical items. Others add intricate machinery. Botania just adds flowers—but wow, what flowers. Flowers that heal you. Flowers that feed animals. Flowers that turn hostile mobs against each other. Flowers that eat cake. Oh, and did I mention that you've can also use flowers to create a magical portal to a world of elves? If you want to try something wildly different from most other mods, Botania is it. Grab it here.
Inventory Tweaks, NotEnoughItems & Waila
[1.7.10]
This trio of mods are essential quality-of-life improvements, especially when you've got loads of mods installed at the same time. Inventory Tweaks allows you to sort your chests with a single click and automatically replace tools when they break. NotEnoughItems provides you with a searchable list of all the blocks available in the game, and the recipes for crafting them, and Waila lets you point your cursor at an unfamiliar blocks to find out what it is. Grab them here, here and here respectively.