Bowman Lake Campground ($15 in summer, $10 primitive camping mid-Sept.–Nov., no reservations) is the largest and most popular in the North Fork. Hiking trails wander off in all directions, including an easy one along the lakeshore.
The campground at Kintla Lake ($15 summer, $10 primitive camping in May and mid-Sept.–Nov., no reservations) is small, with only 13 sites and fewer trails to choose from, but equally desirable.
Both of these campgrounds are fairly developed national park campgrounds, although they don’t have the parking-lot quality of those in the more traveled areas of Glacier.
Other roadside campgrounds a notch down in development are Big Creek (406/387-3800, www.fs.fed.us/r1/flathead [1], $12), a Forest Service campground on the Outside North Fork Road near the Camas Creek entrance to the park, and Logging Creek and Quartz Creek, Glacier National Park [2] campgrounds ($10 July–Nov.) on Inside North Fork Road between Apgar [3] and Polebridge [4]. These are primitive campgrounds; bring your own water.
Links:
[1] http://www.fs.fed.us/r1/flathead
[2] http://www.moon.com/destinations/montana/glacier-national-park
[3] http://www.moon.com/destinations/montana/glacier-national-park/lake-mcdonald-valley/sights/apgar
[4] http://www.moon.com/destinations/montana/glacier-national-park/north-fork-the-flathead-river