The Presidente del Gobierno (literally the "President of the Government") is the Head of Government.
The Presidente del Gobierno is the Head of Government in Spain. The King of Spain nominates a candidate for the presidency who stands before the Congress of Deputies for a Vote of Confidence, effectively an indirect election of the head of government by the elected Congressional delegates. By political custom established by Juan Carlos I of Spain since the ratification of the 1978 Constitution, the King's nominees have all been from parties who maintain a plurality of seats in the Congress.
That seems to me to make him not only the head of government, but the political leader as well.
Therefore the answer to your question is: The current political leader of Spain is the current Presidente del Gobierno, Jose Luis Rodriguez Zapatero.
The following are excerpts from the Spanish Constitution. See the related link.
El Gobierno dirige la política interior y exterior, translated this says that the government directs interior and exterior politics.
1. El Gobierno se compone del Presidente, de los Vicepresidentes en su caso, de los Ministros y de los demás miembros que establezca la ley.
2. El Presidente dirige la acción del Gobierno y coordina las funciones de los demás miembros del mismo, Translated this says that the President directs the actions of the government. Note that the individual's title is President, not Prime Minister, although most English-language news organizations refer to him colloquially as the Prime Minister.