Iona is a "must see". Also, if you can, take the train from Glasgow to Mallaig (West Highland Line) and see some of the most beautiful and rugged scenery Britain has to offer.

Also agree with Glencoe and Culloden. They are very atmospheric.

Fit in the Kelvingrove Museum and Art Gallery in Glasgow too if you can. Recently renovated it's fantastic.

Most of all enjoy. We don't mind Americans really!!!!