Feel free to point towards everything I forgot.
I don't like resource packs, but some people do, so here you go.
Up-to-date
These packs might not 100% up to date, but they are only missing a few textures.
Faithful Modded Edition (Missing GUIs though)(Good GregTech 5, Advanced Power Management, GraviSuite, CompactSolars and Advanced Solar Panels support, very partial Nuclear Control support)
Weed Warning Pack
Weed Warning Pack (Doge Edition)
PureBDCraft: IC2
Partly up-to-date
Soartex Modded (Warning: extremely beefy computer required)(Good GregTech 5, Advanced Machines [Atomic] and Advanced Solar Panels support, partial CompactSolars support)
Zederrian Technology (Strong GregTech 5/6 support, very partial GraviSuite and Advanced Solar Panels support)
Pyrolusite's IC2 Alternate Textures
Minimalist Technology (Previously known as Pyrolusite's GregTech Alternate Textures) (Strong GregTech 5/6 support)
Out of date
IC2 for LB Photo Realism
Isabella II for FTB (Strong Advanced Machines [Atomic] support, good Advances Solar Panel, GraviSuite, Nuclear Control 2 and CompactSolars support)
WIP
IC2 for Fable of Glory
IC2 Modern Resource Pack
Addon-only
Unity (Strong CompactSolars, Advanced Machines [both] and Electro-Magic Tools support)
GregTech Faithful Fanver (Good GregTech 4/5 support)
PureBDCraft: Advanced Solar Panels (Strong Advanced Solar Panels support [duh])
PureBDCraft: Nuclear Control (Strong Nuclear Control 1/2 support)