Here's something I saved from years ago:
If you travel eastward into the Cascades from the Willamette Valley in Oregon, you enter boondocking nirvana. There are several highways that crest the passes, and they all follow rivers. The developed campsites along the rivers are absolutely beautiful, and Oregon state parks are cheap, but if you want to find a gorgeous river/streamside camping spot and you don't need a developed campsite, it's VERRRRY easy to find something nice. I've been noticing this more and more--people just find a place to pull off the road, and set up shop. Frequently they congregate in little informal groups, set up a campfire circle, put up a sat dish, hang out while the kids innertube in the river---good times!
You have to know the backroads a bit, but the best thing to do is EXPLORE---get a map and be prepared to be amazed. There are so many wonderful rivers and streams in the forest, with great places to camp. As far as I know, Mt. Hood Nat'l Forest is the only one of the Oregon forests that doesn't allow "dispersed camping" everywhere--but I've sure as heck seen a lot of it being done there. Here are some specific suggestions:
Mt. Hood area: Salmon River Road, several miles to the road's end. Go east from Welches. Wonderful hiking trail along the river, several established campsites as well as lOTS of booncocking spots. Gorgeous area. Services nearby in Welches. You may never leave.
East of Albany: Take Quartzville Road (BLM Scenic Byway) from Lebanon. The road follows the north shore of Foster Lake and then winds along Quartzville Creek. Great swimming holes!! All BLM-legal dispersed camping, and the road follows the creek for about twenty miles before it continues up into to mountains (great drive BTW), so you can easily find your very own spot.
Continued.. because of some new WEIRD verification page I keep getting stopped at