Heading up the coast from the south:

Damariscotta: The downtown is mall enough to walk around but has a lot of interesting places to see/shop. It's also quite pretty and has a lot of scenic areas within a reasonable drive.

Camden (in the off-season): Bigger but still walkable, also pretty with some good drives nearby, and one of my favorite buildings in the state is there. (Norumbega)

Northport: I love driving Shore Rd and wandering through the old Victorian summer colony.

Belfast: I love the Co-op and the whole downtown area. I haven't been able to walk the footbridge but I love that they have one.

Bucksport: Hate the bridge, love Fort Knox and the downtown. Especially Friars.

Castine: Beautiful, walkable, historic.

Southwest Harbor: Bar Harbor has its points despite the tourists, but when it comes down to it, I like SW Harbor better.

Machias: Okay, I've only been through a couple of times, but there's some good views and a few neat shops here.

Lubec: Only got here once and it was pissing down, but I would like to return and explore it properly. I liked what I saw.