http://glaciers.us/south-cascade-glacierGlaciologists have studied South Cascade Glacier for a number of years. Access is by a rough trail from the CCRR, at a point where it make a major bend and climbs toward the Cascade Pass trailhead.
The Hidden Lake trail gets you quite high, high enough to cross late season snow patches. And in Sept you'll start seeing fall colors (in the heather, etc).
http://www.wta.org/go-hiking/hikes/hidden-lake-lookouthttp://www.wta.org/go-hiking/hikes/sahale-armYes, there are a couple of forest service campgrounds along the CCRR.
It is easier to get to glacier around Mt Baker than in the NC Park complex. On the north side there's Heather Meadows area. On the south side is Railroad Grade.
http://www.wta.org/go-hiking/hikes/railroad-gradeOn the east side of NCNP, consider Hart's Pass, the highest road access in the state. Hikes around Rainy Pass on hwy 20 are worth while (e.g. Blue Lake, Maple Pass, Lake Ann).
Besides the guide books (mainly from the Mountaineers), there are trail reviews at WTA
http://www.wta.org/go-hiking/hikes/maple-pass 
