There is a track at the top of the Lewiston Grade, Summitt Raceway, that is pretty fun for a couple hours. North of Lewiston, about 50 or so miles, you can ride around the trail system that takes off from the Great White Pine campground. Pretty decent riding, not too difficult as far as skill level. If you want to go further north, you can go up to St. Maries and ride at the Christmas Hills rec area. Lots of trails thru there.
Let me know when you come up, because they are supposed to start coming out with maps of the trail system around the Great White Pine. I'll hook you up.
There's also a lot of riding to the south of Lewiston, but I don't get that way much. Mac's Cycle in Clarkston should have a good bunch of contacts for that.