I cannot believe that no one has mentioned Crater Lake! It's a bit out of the way of anything but it's absolutely beautiful.
DSC_0254 by
awilson013, on Flickr
Up the PCH from California through Oregon there are a LOT of very neat places... Too many to even begin to list. There are signs to most of the great ones, and most of them are worth the break. Just don't stop at the "Animal Safari" outside of Bandon or "Trees of Mystery". The animal Safari has a lion that looks like it is 1000 years old and has never been bathed, with dread locks in it's mane. Also a mini-horse thing that literally had mold growing on it's ears. Trees of Mystery is good for a pic with Paul Bunyan, but if you want to walk the nature trail it's like $20/person (maybe more) and NOT worth it. There are some gravel roads through the redwoods outside of crescent city, ca that are pretty neat though... The names are escaping me.
If you can, make a reservation at Ft. Stevens in Warrenton, Oregon. I recommend making it now. From there you'll have access to the Peter Iredale ship wreck, Battery Russell, and the Jetty between the Pacific Ocean and the Columbia River. You can drive from Gearhart, OR all the way to Ft. Stevens on the beach, which is pretty cool if you've never done it. The campground is littered with paved trails that are about 4-5 feet wide, good for a casual bike ride.
In Astoria there is the Astor Column (great for pictures), Ft. Clatsop (great for some education and exploring), and the Fort George (AWESOME for beer and food). The maritime museum there is alright, has a good section on the Coast Guard. There is also a little boat across the street from there called "The Bowpicker" which has the best Fish & Chips you'll ever eat. There'll probably be a line down the street.
From Astoria I would cross over into Washington and take Highway 4 east to I5 and head up into Seattle. I honestly HATE the drive up 101 in Washington, but WA 4 is much better than OR 30, on the opposite side of the river.
I could type on this all day, but my wife is bugging me to go to a movie... If you want, I could continue later.