JR ... in addition to Army Corps of Engineers (most of which have atleast electricity to the site) ... there are literally thousands and thousands of National Forest campgrounds (most of which have no services, not even a dump station).
There are also hundreds of campsites developed by the Bureau of Reclamation, an agency in the Department of US Interior campsites ... most of which have no services and some of which are free.
Three "must have" books are:
2003 Trailer Life Campground Directory
Camping with the Corps
Bureau of Reclamation Lakes guide (hard to find)
A website where you can make reservations or research many National Forest or Corp of Engineer campgrounds, by states:
Once you "pick" an area, like Nick said, you can contact the respective National Forest office ... and for the price of a phone call, pick the forest service folks brain about remote campgrounds ... even occasionally specific campsite recommendations.
We're soon headed to three hand-picked-over-years-of-camping National Forest campgrounds, with reservations for specific drop-dead-beautiful campsites ... but if I told you which ones, I'd have to kill you.
Like Nick says ... like a prospector finding gold. I'll give you generalities, but I've already staked my claim.
Now, for Canada ... I subscribe to Camping Canada ... which publishes an annual campground guide ... which includes many off-other-books campgrounds. To me, it's worth twice the price. We found a remote campground on Prince Edward Island and have returned there many many times.
You can also contact the various Provincial Park areas management. They are always willing to give the specifics about out-of-the way parks.
And of course, in both the US and Canada, you have a vast network of National Parks, running from coast to coast. It's our goal to visit all of them before we die!
Have the fun ... no, 75 percent of the fun ... is doing your homework, checking out new areas, driving campgrounds in the area, writing down campsite numbers for return visits.