Folks seem to always be asking for help finding a vacation rental, so I thought I'd put my 2¢ in for HomeAway.com It's an rental listing site with international coverage; among those are 3000+ Maine listings.
I just used it to book a vacation rental in Europe for this summer, and it was so user friendly. It allows you to make a list of favorites and compare the features of your favorites. A well-thought you, intuitive service. Check it out.