Plenty of choices here, but reservations should still be made as far in advance as possible.
A personal favorite is
Dinosaur Trail RV Resort (11 km/7 mi along North Dinosaur Trail, 403/823-9333, www.holidaytrailsresorts.com [1], May–Sept., $31–48), an oasis of green between the river and the badlands five kilometers (3.1 mi) beyond the Tyrrell Museum. Activities include river floats, fishing, cooling off in the outdoor pool, or exploring the adjacent badlands on foot. Other facilities include horseshoe pits, a playground, a grocery store, and a laundry.
Back toward Drumheller [2], River Grove Campground (25 Poplar St., 403/823-6655, May–Sept., tent sites $25, hookups $29–36) is in a well-treed spot beside the Red Deer River and also offers welcome relief from the heat of the badlands. Serviced sites are semiprivate; tenters have more options and are able to disappear among the trees. The campground offers a nice stretch of sandy beach (by Albertan standards), mini-golf, and an arcade; and town is just a short stroll away.
At the end of the Dinosaur Trail is Bleriot Ferry Provincial Recreation Area ($15) with 28 sites, plenty of free firewood, a kitchen shelter, and a small beach on the river.
Links:
[1] http://www.holidaytrailsresorts.com
[2] http://www.moon.com/destinations/alberta/calgary/dinosaur-valley/drumheller