just north of Cannon Beach is an absolute must-do. They filmed most of the beach scenes in Twilight at Indian Beach, and most of the Goonies coast scenes (where the coast matches the medallion, and where the lighthouse was located) were filmed at the Ecola State Park Overlook. Take the short, mile long trail down to Crescent Beach...because most tourists are incredibly lazy, you will have the place to yourself. We've done this a number of times (usually a little earlier in the year), and have literally had the beach to ourselves. Last time, we arrived at Crescent about 11:00am and didn't see another soul until we were leaving around 5:00pm. It's about the only place on the crowded Oregon coast where you can do this.
If your plans didn't include the coast, Mt. Saint Helens is always fun and educational, and the Columbia River Gorge to about Hood River is an incredibly scenic drive. As a geologist, I find the terrain there incredibly interesting, too. Bagby Springs is a beautiful hike through old growth lowland forest, but, beware of naked hippies.
If you're not married to the idea of staying in Oregon, I'd make a beeline for the Olympic Coast of Washington State. For my taste, the Olympic Peninsula is the most stunning piece of real estate on the planet (rivaled only Glacier NP, and Switzerland). If that's a little bit out of your range, Mt. Rainier National Park is one of my favorite places in the world. Take your family and do the short hike through the grove of the Patriarchs...it's absolutely stunning.
In any event, have a fun trip. The Pacific Northwest is an incredible place.