If you are brave enough to hire a car and take to the wrong side of the road this is a long 2 hr drive. This takes in the best the West Coast has to offer. Road up the side of Loch Lomond is frustratingly windey....the views are worth it. Once into Glencoe the Dramatic Scenery is spectacular.

Version 1 - to Holly Tree Inn
www.hollytreehotel.co.uk/index.html
This is longer but will provide views of the sea lochs. I visited this restaurant last year and the food was Top Notch.
Route
http://maps.google.com/maps?f=d&hl=en&geocode=&saddr=Glasgow&daddr=55.887635,-4.353333+to:Kentallen&mrcr=0,1&mrsp=1&sz=9&mra=dpe&sll=56.266236,-4.754333&sspn=1.073811,2.554321&ie=UTF8&ll=56.266236,-4.754333&spn=1.073811,2.554321&z=9&om=1

Version 2 - to Bridge of Orchy Hotel
www.bridgeoforchy.co.uk
This is not quite as far. Last went here a few years ago and had some pretty good food. Make sure you get further up into Glen Coe to see all the scenery.
Route
http://maps.google.com/maps?f=d&hl=en&geocode=&saddr=Glasgow&daddr=A82%2FGreat+Western+Rd+%4055.892780,+-4.332680+to:56.529199,-4.754333&mrcr=1&mrsp=2&sz=9&mra=dme&sll=56.266236,-4.754333&sspn=1.073811,2.554321&ie=UTF8&z=9&om=1