Here are a few ideas for you. This might not be exactly what you are looking for, but it's a start.

Iron Goat Trail: Contains the ghost town of Wellington, the site of the worst avalanche disaster in our country's history. About 100 people were buried in snow here as they lay sleeping in railroad cars. The town changed its name after the disaster, and was eventually abandoned when the New Cascade Tunnel was built in 1929. You aren't supposed to actually camp in Wellington, but there is camping along the Tye River and official campsites at Money Creek and the Beckler River.

Monte Cristo ghost town: I'm not sure if lots of people lost their lives here, but hey, it's a ghost town. Camping along the river on the way up.

Enchanted Valley/Hoh River Trail: While they most likely aren't "haunted," the Enchanted Valley and the Hoh River Trail are both know for supernatural activity, particularly sasquatch and mothman/thunderbird/garuda sightings. You're more likely to see bears.

Cool question, btw. It's given me some ideas for fall hikes!

Mount Pilchuck's Pinnacle Lake Trail where those 2 female hikers were found dead from gunshot wounds several years back. Still an unsolved mystery. I don't know if there is overnight camping there but, if there is, it's sure to be spooky.

There's Mountain Folk living in the hills around the Mountain Loop highway on the way to Darrington (WA 530). There's also all sorts of free or cheap USFS campsites up there. You want horrors? You'll find them up there. Also, bring weapons, and lots of booze.

There's no such thing as 'haunted.' But, camping is fun regardless, and I definitely second Lake Crescent as a cool place to go.

Far-Flung Woods
http://www.youtube.com/watch?v=ghUD8LRxx6A&feature=related

Lake Janus is supposedly haunted. If you go at the right time there are lots of blueberries near the lake/campsites. No fires.

Lake Janus hike

Is this Ted Bundy? Where ever the fuck you set up your tent is gonna be the haunted forest.

Anyway, the spookiest forest is the side of Mt. Saint Hellens that blew up. Yeah, it's come back a bit, but still scary. Other than that, take a look at the maps of recent forest fires. the big ones. Camping in those places is spooky as hell.

Next up is the Rock Creek/Crab Creek area near a shithole ghost town called "Spokane". That area is scary as hell because it's full of genuine rattle snakes. All over the place. Really. Get out of your car and you will have to be careful not to step on them.

Finally, there's that bit of I5 in Beacon Hill called the Jungle. Set up a tent there and see what happens.

Whoooooooooooooooooo wants to know?

Move along. Nothing to see here.