In Oregon a good 357mag will handle everything but black bears and Mr. or Mrs. Sasquatch...and it might even be sufficient for them (the bears aren't huge here, the Bigfoot are
). It's a really versatile and common caliber, and you can find a 357 revolver in any size that suits you.
My personal choice would be a Glock 20 (10mm). Not that I'm a huge fan of Glock or even 10mm, but it's a nice option for a high capacity, affordable, and relatively lightweight gun with substantial firepower. I personally value the combination of capacity and light portability when trouncing around in the woods, as I tend to cover a bit of ground.
I live in Oregon (Douglas County it just so happens), and the G20 is my preference. But the 357mag might be the more practical and versatile option for a lot of folks.