Screw reading this whole thread, I'm feelin lazy today.
My take on this question is as follows:
No, Corporations are not persons.
However, corporations are simply groups of persons who decided to incorporate themselves for tax and other reasons.
Thus, IMO, it would follow that:
Corporations, as a grouping of persons, can, if directed by an individual and/or consensus of individuals who own/run said corporation, exercise a form of freedom of speech by contributing to a candidate or candidates whose policies they feel will benefit them.