You could quite easily construct yourself a nice trip to Islay: something like Glasgow - (train) - Ardrossan Harbour - (ferry) - Brodick - (bus) - Lochranza - (ferry) - Claonaig - (bus) - Kennacraig - (ferry) - Port Ellen - (bus) - Port Askaig - (ferry) - Oban - (train) - Glasgow, stopping plenty (including an overnight) inbetween times. You'd get a great impression of the islands that way.

flybe also do Glasgow to Islay flights, which aren't too expensive, if you wanted to do a day trip (or shorten one of the directions).