Gifford's is the place to go for ice cream, hands down. It's a great place to stop for dessert (or for a special treat on a hot day). The ice cream is delicious and generously scooped. There are so many tasty flavors to choose from that I usually end up getting a double because I can't choose just one. I especially recommend the Maine-centric flavors like Maine Wildberry and Maine Black Bear. (They have a sign identifying these flavors immediately to the right of the windows where you place your order.)
Gifford's is easy to find and has ample parking. This is an old-school ice cream stand, where you order outdoors (albeit under a roof). There is no indoor seating, just the picnic tables around back. I've generally found the staff to be friendly and pretty efficient at fulfilling my order. Gifford's is immensely popular with the locals, so expect a line on a hot day. Note that this is a seasonal restaurant. I think they are closed roughly late October through late March.