Yellowstone Grizzly RV Park:
www.grizzlyrv.com, 406-646-4466. We've stayed there several times and like its location, close to the business district of West Yellowstone and just minutes from the west entrance to the park.
I need to add that we've never tried any of the other places in and around West Yellowstone; we do have friends who have stayed at and really liked the KOA campground just outside of town. If you're making reservations online, be careful if the park/site descriptions are sketchy and you can't see any pictures of them or a map of the park. At least 2 of the places we did check out in town looked like packed tins of sardines--crowded, very small sites, very difficult to wiggle into a lot of the sites (or so it seemed to us). The Grizzly RV Park is nice and wide open, with paved sites, landscaping, and lots of room.
Carolyn
NOTE: I just compared prices between the Grizzly RV Park and the Red Rock RV park. Next time, we're going to give the Red Rock park a try. Its prices are about half of the prices for comparable sites in the Grizzly RV Park. Even though it's a bit out of town, the scenery in the area is so pretty that we won't mind having to make that drive into West Yellowstone a couple of times while there.