There is no official association equivalent to the Académie Française. The nearest we have to an authority on the language is the Oxford English Dictionary, which is regularly revised and updated to accommodate changes in usage and new vocabulary. Though of course, other dictionaries, such as Cambridge, Macmillan and Collins are equally reliable. For US English, the Merriam Webster is the most widely used dictionary.

I consult the Encyclopædia Britannica Online and its items are considered reliable, accurate and well written.