We stayed at Fishing Bridge inside of Yellowstone in June. If we had it to do over, we'd have bought a generator and stayed at Madison or Norris campgrounds inside of the park. Much prettier parks with larger sites. But Fishing Bridge did serve our purpose. We stayed 10 days inside of the park. There's a really nice travel book, I think you can find it on
www.travelbrains.com. I found it at one of their general stores on the last day of our trip. Just my luck :-) Wherever you stay you will enjoy Yellowstone.
Here's a good forum on Yellowstone. They post topics such as "Bear Sightings 2008". From what we saw, these posts are fairly accurate and if somebody saw a bear, you will probably see it there again. They seem to be creatures of habit and near the same places each time.
http://www.yellowstone.net/forums/
We also stayed in the Tetons and then drove to Jackson Hole. Colter Bay RV park was a nice campground on a beautiful lake. Jackson Hole is about a 30 minute drive away.
The avatar picture you see is of our camper at Fishing Bridge. If you click on the picture, you'll see what happened a few days later on June 6. So be prepared for any weather.