I am sure I don't know about all of them, but here are the ones I am aware of and which seem fairly reliable (others do rather tend to come and go I fear). It can be nice to have a look at the weather, or the number of other boats around, or whether someone you know is strolling by hand-in-hand with someone he or she did not ought to be.
Oban: Oban North Pier
Craignure, Sound of Mull: by the ferry terminal
Dunstaffnage, Lower Loch Linnhe: over the bay
Fort William, Upper Loch Linnhe: OK