The coast is a must. Gold Beach, Coos Bay, Newport, Austoria would all be on my list. Also Multnomah Falls area just out of Portland offers some light hiking with great views of the Columbia River. I will post pics when I get home.
I have to agree with Morgan. With the coast it just depends on if you like crowded or mellow. I have to say that Seaside is one of the most visited.
As for the hiking, Multnomah Falls is a very nice area. If you are staying in the portland area for a couple of days try the ape caves up by Mt. St helens. It's in Washington but a real nice area
My wife wants to visit Oregon, as well as Montana. I think we can do both on one trip. She likes to fish, as do I. We might also do some hiking and such. Any suggestions welcome.
Central Oregon is great for fishing/hiking. The Metolius river is world famous for its fly fishing. For hiking, I'd suggest doing visiting Sahalie and Koosah falls and the Blue Hole on the McKenzie river. Finish up with the Bend Ale Trail
The time of year could make a difference. In the spring all the waterfalls in the Multnomah falls area are raging and beautiful. There are a bunch in the area so lots to hike around and see. Later in the summer they aren't quite as spectacular but then you can got to the Oregon Gardens or head for the coast.
Fishing depends on what you want to pay for being out of state and what type of fish are you after.
Crater lake is awesome, but if your visiting in the winter it will be closed due to snow. I would agree with visiting the coast. I love taking a boat out into charleston or winchester bay and fishing for crab. pretty easy and we always get some nice dungeness this time of year. also you could ride the dunes.
Central Oregon is very nice, with some great rivers for fishing and beautiful scenery. I haven't been to Montana but I get the impression it has some similarity to Central Oregon. If you want the full experience I suggest going a little more west, over the pass, and you get quite a different experience. Less evergreens and meadows, and more dense greenery with a larger variety. If you could make it all the way to the coast you would not regret it, nor would you the Multnoma Falls/Columbia Gorge Area.