I spent the summer paddling the downeast Maine coast from Cobscook Bay area to Mount Desert Island. The following are what I consider to be the best day trips along that coastline. Note all these trips were made in benign weather conditions. Your mileage may vary.
Mount Desert Island: Bar Harbor to Seal Harbor. This coast has 20-100+ cliffs the entire way with several mountains towering in the background and Frenchmen's Bay in the other direction. Erosion has created many caves, grottos, canyons and other interesting formations. I dunno, I guess it's 8-10 miles one way. I put in at Bar Harbor and poked along for 5-7 miles or so one day and then put in at Southwest Harbor another day to finish that particular section.
Frenchmen's Bay: The Porcupines & Ironbound Island. There are 5 small islands scattered closely together just off of Bar Harbor, collectively called the Porcupines. Each of them has tall 50+ cliffs on the seaward side and then taper off with forested slopes. Ironbound Island lies just off the Porcupines and is much larger. It's southern coast is pink granite cliffs while the northern coast is 100+ cliffs that (to me) are even more impressive than the trip mentioned above. If you're lucky you'll get several bald eagle sightings. You may also see seals, porpoises and at least have the opportunity of a minke whale sighting. I saw large beds of baby mussels, lots of red starfish and sea urchins. These islands are also easily reachable from South Goldsboro on the Schoodic Peninsula on the other side of Frenchmen's Bay.
Schoodic Peninsula: is the north shore of Frenchmen's Bay. Shorelines on both sides of the peninsula are 20+ foot pink granite cliffs extending 5-6 miles. Schoodic Point is a series of ledges and cliffs reaching out into the ocean a hundred feet or so. Because of their layout, these ledges cause waves to pound the point with extra force shooting geysers of spray into the air. During some storms they go as high as 40 feet. It's also a good day trip by car when strong winds from the east cause extra wave actions. I found a nice put in down a tiny road in a small cove just before you reach the point itself. Note you may have a short carry at the mouth of the cove at lower tides or there may be strong currents during mid-tide. There are also potential put in sites on the far side of the peninsula.
Machias: Rouge Island. This is a private island in Englishmen's Bay that may be 10 miles or so around. I put in from Rogue Bluffs State Park and the near side of the island has pretty dramatic cliffs leading to a headland. The rest of the northern side of the island is pretty but not spectacular. The southern side has steep, ledge and tree covered slopes on which I saw a deer. The southeast side has several small islands with 50+ foot forested cliffs clustered into a beautiful landscape. The east coast consists of continuous 20-50 foot pink granite cliffs.
Jonesboro: Great Waas Island. The north and east sides of this island are 20-50 foot cliffs of pink granite. I came across a colony of around 250 seals sunning themselves on one of the outer points. I didn't have time to circle the island so don't know the south coast. The west coast is fronted by Beals Island which is pretty much a working harbor type island. Note there are many smaller island in the bay to the north of Great Waas ready to be explored also.
The Cobscook Bay area is not on the top 5 simply because it takes several days to do this area justice. With many quiet, peaceful, protected connecting bays to explore there is a lot of enjoyment to be had here. Each bay has it's own different beauty. You'll soon loose count of the bald eagle sightings, should see several active nests and encounter many seal colonies.
Wannados still include the Cutler Coast in Cutler, which contains 5+ miles of beautiful, rugged coastline and West Quoddy Point in Lubec with more 100 foot jagged and rugged cliffs.