http://www.cannonbeach.org/
Try to take in nearby Seaside, as well:
http://www.seasideor.com/
Seaside is a little "busier" of the two locales. Each has appeal. The worst I can say about either is the nice-weather-window is short - maybe ~3 months out of the year (well, "nice" to me .
), but that's likely a non-issue for you since it's summer. Have fun!