What is the ruling on one who swears by other than Allah? Is that considered disbelief (kufr)? And if he repents, what happens to his good deeds performed before swearing by other than Allah? What is the ruling on swearing by "the life of Allah," "the honor of Allah," or "the might of Allah"?

Swearing by other than Allah is minor Shirk (definition) (polytheism) that does not expel one from the fold of Islam, unless the swearer intends to glorify the one sworn by as Allah is glorified. There is no expiation for it. As for swearing by the attributes of Allah, such as His Might, Power, Grandeur, and so on, it is permissible, and expiation is required if one breaks the oath.