Who is the president of Andorra?

Andorra doesn't have a president. It has two co-princes. One is the head of the French government; the other is the Bishop of Seu d'Urgell in Spain. There is also a Parliament. The elected head is considered the head of government. His (or her) term is four years.
Principal Government Officials in 2009
Co-Prince--Nicolas Sarkozy, President of France
Co-Prince--Joan Enric Vives i Sicilia, Bishop of Seu d'Urgell, Spain
Head of Government--Jaume Bartumeu
Andorra is a Principality, there is no President. Please check the related link for details.
Update as of 2014:
chief of state: French Coprince Francois HOLLANDE (since 15 May 2012); represented by Christian FREMONT (since September 2008) and Spanish Coprince Archbishop Joan-Enric VIVES i Sicilia (since 12 May 2003); represented by Nemesi MARQUES i Oste (since 30 July 2003) head of government: Head of Government (or Cap de Govern) Antoni MARTI PETIT (since 12 May 2011) -next election April 2015
Andorra doesn't have a President. It is a Co-Principality, with two Princes as Head of State. These are ceremonial positions, which have no real power. The two Heads of State are the President of France and the Bishop of Urgell in Spain.

The Head of Government (Cap de Govern) of Andorra is currently Jaume Bartumeu Cassany of the Social Democratic Party (Partit Socialdemòcrata).
Andorra has a Prime Minister, Jaume Bartumeu.