OK, so this isn't Orkney, or even Kilmartin Glen which is a bit too far from any of the anchorages to be easily visited, but there is still a lot of stuff around. I am not quite sure where archaeology ends and history begins, but who cares, this is what I think there is to see:
There is only one stone circle (Loch Buie, South Mull) in the area.
There are a few standing stones to admire and lean against: East Tarbert Bay, Gigha; Onich at the entrance to Loch Leven; near the South Pier on Gigha; Loch Stornoway, Kintyre; on the Glengorm estate near Loch Mingary, West Mull; and Loch Cuan, West Mull. And there is the strangely named but not very exciting Ogham Stone near Ardminish Bay, Gigha.
There are cup and ring markings at Sailean Mor, Kintyre as well as at Port an Dunain, Loch Leven, and an iron age fort at Little Horseshoe Bay, Kerrera as well as some sort of defensive structure on Loch Scridain.
On Canna you will find a Viking grave and a souterrain but they are both a bit of a walk from the anchorage.
And at Oitir Mhor on Kerrera there is the almost invisible remains of the Cladh a’Bhearnaig monastery.
There are only two brochs - the most complete is a bit of a walk from the Gott Bay anchorage on Tiree, and there is a more ruined one on Lismore.
There are separate pages for castles, ecclesiastical things and other buildings of interest.