Kob, Iam...is right on pointing you towards the Snake River. There's tons of Mulys down there. If you have a boat there is a really good spot just downstream from Blyton (sp?) landing about 5-6 miles upstream from wawwai park and still a bit upstream of granite point I believe. There is a large canyon in there that goes back in a lonnggg ways and branches out from there into several side canyons. You can easily spend a full day in here and only work one of the canyons. The only trick here is that you need a boat to get across but don't expect to ba alone as there will usually be a lot of people down there on openning day (Hint: wear lots of orange). This used to be a "feel Free To Hunt" area and I'm sure it still is.
I have seen some dandy bucks in this canyon but after the first weekend they get amazingly scarce.
Other decent places that havn't been mentioned would have to be the tucannon river area and the blue mountains to the south. There is also some feel free to hunt areas just out of colfax on the palouse river but you will probably only see some monster whitetails out there so I wouldn't go. hehe.

Go explore and have fun!!

Duke