No one knows, because everyday there might be a new answer put in that is longer than the one before it.
So far the longest answer found seems to be "How many countries are there in the world?" Other long answers on WikiAnswers are listed below in the related links section of this answer.
longest what?
longest what?
The longest song ever in the USA was 75 minutes
Shakespeare's longest tragedy and longest play is Hamlet.
Rita is the third longest after emily been the second longest and ken been the first longest
limousine is the longest car
Equator is the longest latitude.
a dam is the longest in Asia
the longest orbit is pluto
Eastwest is the longest library.
probably at the longest beach
mississippi