I vote for Orcas Island. We bought property there because we thought it was the prettiest.
Have a romantic dinner at the Inn at Ship Bay
http://www.innatshipbay.com/ Our friends who live on the island claim it's the best. Reservations required. They have a beautiful setting on the water and really pretty gardens so go early so you have time to look around. Nice place to stay too and not too far from Eastsound.
Another really nice place to stay is Spring Bay Inn
http://www.springbayinn.com/ if you and your significant other are athletic and would like to take a morning kayak trip. New and clean and right on the water but very isolated.
There are lots of highly rated B&B's on the island. Blue Heron,
Kangeroo House,
Kingfish Inn, Old Trout are all on the water and at the top of the list at tripadvisor.com.
The Outlook Inn is right in Eastsound and is quite nice. Especially good if you don't bring your car tho you might want to eat at Christine's
http://www.christinas.net/ instead of Spring Bay since you can walk to Christine's. (There's a shuttle from the ferry landing so you can leave the car and save yourself the hassle of the ferry lines.)
The Turtleback Farm Inn is not on the water but is in the book "1000 Places to See Before You Die."
For a smaller budget try the
Cascade Harbor Inn or perhaps the Blackberry Beach Cabins if you can get their waterfront cabin. http://www.blackberrybeach.com/ I've stayed at both and they both have beautiful views.
