I agree with Gregory and Michael that doing and Adwords campaign can be a good way to start. Also remember that the various keyword tools do not take seseanality into account but agregate the search into a 12 month average.
When doing keyword research through Adwords also remember that a large part of the clicks fall in the adwords section and not the organic section, so a pos 1 in organic will not give you the same amount of clicks as pos 1 in adwords for most search terms.
