NW Oregon Coast
We spent last August in this area and fell in love with it. As others have mentioned, this whole area of the Oregon coast is exceptional, and August is the perfect time to be there. Seaside is a cute classic beachside town, with everything you'd expect (good food, junk food, an antique carousel, small shops, a very good information center, and of course, the beach). It can get a little congested, and the volleyball tournament mentioned above really takes over the town during that week, which may either be good or bad depending on your interests. There is a fantastic bagel shop at the end of the main strip when you're looking for a simple, good breakfast or lunch.
I definitely recommend exploring the areas 30 minutes or so north and south of Seaside (several mentioned in other comments). South, Cannon Beach is stunning and has some extremely unique and towering natural rock formations. Ecola State Park is possibly one of the most goregous hiking locations in the country, even the long, winding drive to the trailhead feels magical. North, Astoria is a very cool port town with lots of history and my favorite coffee shop in the country, Coffee Girl. It is housed inside the oldest cannery building in the west, right on the Columbia River, so you can sit outside and sip coffee and watch huge cargo ships go buy as sea lions play on the rock jetty. Astoria also has a tower you can climb to the top of and fly balsa wood planes from ($2 in the gift shop), which was one of our trip highlights.
We also did a lot of kiteflying, and attended the kite festival in Long Beach mentioned above, which was incredible. We're not surfers but this area is also known for excellent surfing and lots of places offer lessons and rentals.
Anyway, as you can gather, we fell in love with the place and I suspect you will too! Feel free to ask if you have any specific questions, we basically lived there for a month so got to know the area quite well.