If you start in Astoria, there are three forts that guarded the mouth of the Columbia River, two in Washington (Canby and Columbia), and Stevens in Oregon. The wreck of the Peter Iredale is on the beach at Fort Stevens. Lesser known fact is Clark Cable did some acting in the Liberty Theater in Astoria in his early career.Astoria/Warrenton is where Lewis and Clark wintered, and there is a nice interpretive center to visit. The L&C center at Cape Disappointment on the WA side is very nice, and also has a history of the light houses at the mouth of the Columbia River (and the original Fesnel lens used in two lighthouses).
Going south, Seaside is a tourist trap, Cannon Beach is a tourist trap... I like the Manzanita area (and Nehalem Bay State Park for camping). If you can spare the time and like to hike, the climb to the top of Neah-Kah-Nie Mountain is well worth the stunning vista on a clear day. Bring your treasure hunting skills, native legend tells of a pirate ship wrecked on the rocks and the treasure buried somewhere. Many have looked for it, but it hasn't been found. Also watch for beeswax left by another shipwreck (we have a small piece found many years ago). Heading south, the Tillamook Creamery is a must see tourist trap. The Air Museum is also well worth seeing (the engine display is my fav). A drive around Cape Kiwanda is great, and there is a wreck of a B-17 bomber out on Tillamook Head if you care to hike out to it.
I could go on and on, but you get the idea. There is much to see and your week will be full... and you will want to come back. If you can go during the whale migration, all the better, the gray whales are becoming quite common (at the north entrance to the road that leads to Cape Foulweather, I've seen nearly 20 whales right off the rocks, all feeding in and around the kelp beds. Oh, and if you get to Newport, be sure to stop at the Hatfield Marine Science Center, the Oregon Coast Aquarium, AND, most importantly, the WORLD Headquarters of the Rogue Brewery.
Have a wonderful trip!!
Steve