1. I was purposely trying to find stuff that wouldn't be seen as OP, since silicon is infinite.
2. Look at the original post for future fusion reactor recipes. Some day, Manganese + Hydrogen = iron.
EDIT: Sorry for all the edits, I just have things coming to me quickly...
Also, coming up with fusion recipes is getting kinda fun!
Beryllium (Be, 4) + Nitrogen (N, 7) = Sodium (Na, 11) (So basically, infinite sodium from ender pearls and/or saltpeter. Combined with my above suggestion plus your planned manganese + Hydrogen = iron recipe, this could be quite useful. Basically you could make iron from ender pearls, sand, and water.)
Hydrogen (H, 1) + Helium (He, 2) = Lithium (Li, 3) (Okay, so this one is kinda useless given how valuable helium is....)
Iron (Fe, 26) + Helium (He, 2) = NIckel (Ni, 28 ) (Just seems appropriate that they be related in the fusion reactor)
Silicon (Si, 14) + Sulfer (S, 16) = Zinc (Sn, 30) (Zinc from sand and sulfer, seems appropriate)
Iron (Fe, 26) + Iodine (I, 53) = Gold (Au, 79) (Is Iodine in Gregtech?) or Copper (Cu, 29) + TIn (Sn, 50) = Gold (Au, 79) (I just thought this one was kinda funny. :P)
Magnesium (Mn, 12) + Hydrogen (H, 1) = Aluminium (Al, 13) or Sodium (Na, 11) + Helium (He, 2) = Aluminium (Al, 13)
Zinc (Zn, 30) + Calcium (Ca, 20) = Tin (Sn, 50) (Zinc and tin are already associated, so why not?)
Oxygen (O, 8 ) + Oxygen (O, 8 ) = Sulfer (S, 16) (It's so abundant at the point you have a fusion reactor, you might as well just let it be infinite, at the cost of energy. Plus, it can be combined with my above suggestion of Silicon + Sulfer = Zinc, which can then be combined with Calcium to get tin)
Aluminium (Al, 13) + Sulfer (S, 16) = Copper (Cu, 29) or Calcium (Ca, 20) + Fluorine (F, 9) = Copper (Cu, 29) (Ignore this if fluorine isn't in Gregtech) or Magnesium (Mg, 12) + Chlorine (Cl, 17) = Copper (Cu, 29)
Gold (Au, 79) + Hydrogen (H, 1) = Mercury (Hg, 80) (FINALLY, uses for all that infinite gold!)
Mercury (Hg, 80) + Helium (He, 2) = Lead (Pb, 82)
Carbon (C, 8 ) + Lead (Pb, 82) = Thorium (Th, 90) or Gold (Au, 79) + Sodium (Na, 11) = Thorium (Th, 90) or Tungsten (W, 74) + Sulfer (S, 16) = Thorium (90)
Thorium (Th, 90) + Helium (He, 2) = Uranium (U, 92) (Assuming you keep this at a 1:1 ratio by using cells, this will always be a lossy process. Or you could leave it as dusts and increase the energy requirement, or just not use this at all, but that's all up to you.)
Just noticed that Radon (Rn, 86) can be combined with Beryllium (Be, 4) to make Thorium (Th, 90), Carbon (C, 6) to make Uranium, and Oxygen (O, 8 ) to make Plutonium. Perhaps this could lead to some interesting mechanics involving radon extraction from the air? Or perhaps radon cells could simply be compressed and used as extremely weak but infinite reactor fuel?
Oooor, perhaps Radon could be an element acquirable only through the fusion reactor? Looking for good recipes now..
Wolframium (W, 74) + Magnesium (Mg, 12) = Radon (Rn, 86)
Gold (Au, 79) + Nitrogen (N, 7) = Radon (RN, 86)
Mercury (Hg, 80) + Carbon (C, 6) = Radon (Rn, 86)