Henry Hardy gives an illuminating account of Isaiah Berlin's pluralism, an idea he developed as a result of reading Machiavelli. Hardy knew and worked closely with Berlin for many years, and continues to edit and publish his papers. As well as giving a very clear account of Berlin's thought, he gives some insights into what kind of a man Berlin was.
In passing Hardy also reveals that Tony Blair once wrote to Berlin looking for an intellectual ally...
Listen to Henry Hardy on Isaiah Berlin's Pluralism
Visit the Isaiah Berlin Virtual Library (an excellent resource - includes bibliographies, transcripts, an audio recording of Berlin and the text of Tony Blair's letter)