Depends on what you want do to.

You could take a trip out towards Bend in central Oregon and cruise the gorgeous Cascade Lakes Scenic Byway, then grab a beer at the Deschutes Brewery.
Or drive down the Columbia Gorge, take a hike to the top of Multnomah Falls, and have an ice cream cone when you're done.
Or check out Mt. Hood and historic Timberline Lodge.
Low tide at Haystack Rock in Cannon Beach is always fun, where you can see tons of starfish, sea anemones, and the like up close. There are many beautiful beaches and quaint towns on Oregon's coast and some interesting sights like the Oregon Coast Aquarium and the Sea Lion Caves.
Crater Lake is a truly spectacular sight although it's far to the south.
Then there's Silver Falls, Smith Rock, the John Day Fossil Beds, etc...
Basically, Oregon is laden with natural beauty of all types, especially if you're willing to drive a little ways.
Portland is very clean, easy to get around in, and fun to explore, although it does not have many "tourist attractions". There are some great restaurants and decent nightlife in Portland, and a lot of natural beauty even within the city.
Best bet is to stop by a bookstore or library and check out some Oregon or Portland travel guides, and prioritize the things you want do to or see. I think this is a great place to visit.
