There are a number of websites devoted to the Parthenon Marbles, mainly concerned with their restitution to Greece. Try The Parthenon Marbles web site. Or try this site, set up by Greek Students studying in Crete.
The Parthenon Marbles, however, are currently displayed in the British Museum. After a long time of being called the Elgin Marbles, the British Museum now refers to these relief sculptures as the Parthenon Marbles, and recognises the debate concernng their keeping in the Museum on a special web site. here you will find a detailed account of the Parthenon Marbles from the perspective of the British Museum (look at the section titled The Parthenon Sculptures: facts and figures on this site). It provides a detailed account of the acquisition and treatment of the Marbles since 1801.
Try comparing these sites. The first two are emotive and present moral reasons for the return of the Marbles. The British Museum site is factually correct, but glosses over the moral reasons for the return of the marbles, and argues instead for the need for a World Museum - which of course fits the british Museum's view of itself very well.