MineTweaker (requires MTUtils)
Et Futurum (that Mod adds some 1.8+ content to 1.7.10)
Binnie’s Mods (requires Binnie Patcher aswell, if you use Forestry 4)
IndustrialCraft² Classic (by Speiger)
JABBA (But GT6 does replace it entirely basically)
Mystcraft (be careful with installing it and set "useconfigs" in the "core.cfg" at the "baselining" category to true, I had to hard-restart my Computer, because of the insane Lag it caused when it was set to false, and I have 8 GB of RAM assigned!
Thaumcraft, requires Thaumic Fixer and Baubles to work!
Biomes o' Plenty
Tropicraft but make sure you unzip its contents before you install it!
Underground Biomes (GT Ores can generate in its Stone seemlessly)
Per Fabrica Ad Astra (all of its Ores have processing chains)
Fossils and Archeology
Wastelands (needs to be selected in the World Options in order to generate)
Modular Force Field System (MFFS)
Open Modular Turrets
Balkon’s Weapon Mod
Pams Harvestcraft (tons of recipes were improved through my Machines)
Growthcraft Community Edition
Spice of Life
Enviromine (Hydration and Temperature)
RotaryCraft, ElectriCraft, ReactorCraft
All of this plus plenty of Books from several Mods that I needed to be able to place them in Shelves, and some Mods I might have forgotten.