How much time do you have and what are your interests? There are 3 possible routes.
You could go up the oregon coast and load up on tidepools, seastacks, lighthouses, hiking and cool towns. Things I would consider are the Redwoods (North CA actually), Bandon (town and seastacks), Cape Perpetua (coastal features), Newport (town, Aquarium, Hatfield Science Center), Depot Bay (whale watching), take 3 capes loop road and have a beer in front of a seastack at Pelican Brewing, Tillamook Cheese Factory, Manzanita (town and beach), Cannon Beach (town, seastacks, Ecola state park), Astoria (town, column, food, beer, river views).
If you go up I-5 I'd consider Ashland (town, food, see a shakespear play), Jacksonville (old west town), you'll pass 3 valleys full of vineyards, Silver Falls State Park (short hike to tons of waterfalls).
If you go up the dry high desert side of the cascades on 97 you can load up on views of volcanos. Things I would consider are stopping by Crater Lake National Park, geologic features near Fort Rock or Newberry Crater, take in the views off the Cascade Lakes Highway, Bend (food, beer, floating the Descutes River), visit Smith Rock and maybe the Cove palisades. Then you can get to Portland either by 1) going over Mt. Hood (hiking, views, drive up to Timberline Lodge, or 2) go up to Hood River (town, food, beer, views), and drive through the Columbia River Gorge (hiking, views, massive # of waterfalls many can be accessed a few feet from your car).
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Take US95N along the eastern side of California's Sierra mountains. You'll go right by Death Valley which might be worth a look. Take a detour through the back door to Yosemite National Park one of the prettiest mountain drives in the USA. From Reno take a detour and drive the road around Lalke Tahoe for more amazing views. Instead of going through Eugene, veer to the right on Highway 97 and stop in Bend Oregon, a lovely spot.