Recommendations for Maine

I know some of you visit or live in Maine, so I present the following for my (and my brother's) edification:

My brother and his wife are planning a trip to Maine, likely this summer, for their 10th anniversary. They're looking for places to go. My brother dearly loves wild areas, and the one thing currently on his list is Acadia National Park.

Any suggestions on where else? Referrals to other people welcome.

Thanks!