I already have quite a List of Fusion Reactions in GT6, though most Materials it makes are only really useful for more Fusion. Tritium and Deuterium can be useful for Breeding in the Reactor though, so I guess that would be a way to make use of some of the reactions.
The only really useful thing I can make (because i am bound to realism in some aspects), is all those magical made up Elements that typically show up in Pop-Culture. 
So I might add an Aneutronic Fusion Reactor that is portable kinda like Iron Man has, and use Materials you can only get via Fusion to craft it in the first place.