We stayed at Grizzly RV Park (406-646-4466 or www.grizzlyrv.com
) in the town of West Yellowstone, Montana. This private park was the nicest campground in the area. It is the most efficiently designed campground I have seen. The people running the park were very helpful. Though their prices were a little high, around $42 with AAA discount, you have full hookups, cable tv, and WiFi. Plus your in walking distance to the shops of West Yellowstone.
If your looking for less expensive camping, there is a campground in Gallatin National Forest just three miles north of West Yellowstone on US 191. Bakers Hole (406-646-7369) is located on the Madison River. About half the sites had water and electricity. Pit toilets only.
We did look around at a number of campgrounds in the area, but these two were by far the best. There also was a KOA outside of town that wasn't bad, but their prices were higher.