"The true value of a man is not determined by his possession, supposed or real, of Truth, but rather by his sincere exertion to get to the Truth. It is not possession of the Truth, but ratherthe pursuit of Truth by which he extends his powers and in which his ever-growing perfectibility is to be found. Possession makes one passive, indolent, and proud. If God were to hold all Truth concealed in his right hand, and in his left only the steady and dilligent drive for Truth, albeit with the proviso that I would always and forever err in the process, and to offer me the choice, I would with all humility take the left hand, and say: Father, I will take this--the pure Truth is for You alone."

Virtually anything that instigates cerebral activity and makes me go, "hmm".
I.e.; Philosophy, Politics, Sociology, Religion, Mormonism, etc.