Version 2.1.8 - Recommended
Website: http://ae1.ae-mod.info/
Store items as energy patterns in complex computer networks.
Make huge ships and sail them through the water and the air.
Lots of aesthetic blocks to make your builds look good.
Adds useful camera functionality to Minecraft for animation.
Provides basic functionality for ChickenBones's mods.
Provides basic functionality for Team CoFH's mods.
Website: http://www.computercraft.info/
Provides computers, turtle robots, and more, all based on the Lua programming language.
Spotlights that shine for up to 64 blocks, made especially for Direwolf20.
The mod that brings the wonder of the Stargate to Minecraft!
Website: http://industrial-craft.net
The original Minecraft tech mod. You probably remember this from Tekkit Classic (1.2.5). Sometimes it's only used for its API, sometimes it's used fully.
Website: http://www.minecraftforge.net/forum/
The pack's mod API, Forge. (Also used in Tekkit and FTB.)
Website: http://calclavia.com/mffs/
Use electricity to generate force fields and keep your stuff safe.
Website: http://www.machinemuse.net/
Create an Iron Man-style suit and modify it with all your favorite extensions.
A GUI to show you recipes and uses for every item in the game.
Website: http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/1293018-opencomputers-v1-4-2
An open-source ComputerCraft alternative, this adds programmable computers and robots to the game.
A fully rewritten replacement of Eloram's RedPower 2 mod.
Website: http://resonantengine.com/
The successor to Universal Electricity, this provides a common API for tech mods.
Adds a variety of realistic guns and ammo.
A rebooted version of the Wireless Redstone mod, with 3D models and better mod integration.
Tools for building and clearing large structures.
Many magical items involving armor, weapons, and special abilities.