I'm also in Corvallis Oregon, and highly recommend it
I was born here, went to PS here, and am just now beginning to unschool my DS here. Corvallis has - a small town feel, doesn't get too cold (I don't think I've ever seen it below 20 degrees here) and has great summer weather. Also, within an hour and a half you have: the mountains, including the PCT (pacific crest trail) Silver Creek Falls (a easy hiking trail 7.5 miles long with 7 waterfalls!) as well as many other waterfalls, large and small (Salt Creek Falls is the second tallest in Oregon, and offers many hiking trails, other waterfalls to see). Also, the beach is about an hour away, including the well-known Oregon Coast Aquarium, which is a learning-oriented aquarium, and has many places to camp (legally, or on the beach if you want to chance it - I've camped on the beach many times and never had any issues).
There's also Eugene about 30 minutes away, which has some great music venues, and Portland, about 1.5 hours away, which has the Oregon Zoo, OMSI (Oregon Museum of Science and Industry), which is completely kid-friendly, and Powell's Bookstore, the largest bookstore in the world.
Corvallis also offers a large Farmer's Market that runs mid-April until the weekend before Thanksgiving. You can also buy cheeses, meats, wine and other foodstuffs at the Market.
Corvallis is a very intellectual community, with events such as da Vinci Days, a local, 3 day long festival of vendors, music, and science-y type events and booths, as well a a parade of 'da Vinci's machines.' We have a really big library, an arts center where kids can take ballet, ceramics, and other class for about $60 a term, and a sports park, which offers soccer, among other sports for kids, for about $50 per term (14-16 lessons).
Anyway, if you couldn't tell, I love it here, and highly recommend it, so long as you don't convince a bunch of people from California to move here
Also, there's a big, supportive group of unschoolers in town, who try to get together often. We're crunchy, artsy, laid-back, fun people around here
I think Corvallis is cheaper than Eugene - you can rent a 3 bedroom house here for under $1,000 in a nice neighborhood with a big backyard, but I don't think you could find that (in a nice neighborhood) in Eugene, based on what I've heard.