If you are interested in finding out about the Lords of the Isles, The Lords of the Isles: Clan Donald and the Early Kingdom of the Scots by Ronald Williams might be a good place to start... its readily available in book shops, especially those that sell them off at a fraction of the cover price, or Amazon! Alternatively, wikipedia has fairly reliable info!
You're right when you state that Clan Donald originated Islay; the clan takes its name from Donald of Islay, the son of Ranald who in turn was the son of Somerled. I guess its true that somewhere along the line "descendants" of Donald of Islay started selling burgers! In fact it was Dick and Mac McDonald who started the company; their father immigrated to America from Ireland, while there is also speculation that they are also descended from the Glencoe MacDonalds... and the founder of that clan was the son of Angus Og of Islay while another of his sons was the first Lord of the Isles! Kind of come full circle hasn't it?
Here is a few pictures i took up at the Finlaggan. Not the best weather nor the best photographer. But it was a very impressive scenery, and i really hope to be back there one day. It must have been a real impressive site back in the days.
The Maggie is one of Ealing studios lesser known comedies. A wily old skipper of a Western Isles 'Puffer' and his motley crew lead all who come into contact with them a fine old time! Many scenes on Islay!