Here are some suggestions (we were in Yellowstone/Tetons/Jackson) a few weeks ago:
1. Lake Yellowstone Hotel dining room - Given that there are few good dining options in the park, this remains a good bet for solid food. I'm not saying it's phenomenal, and if you're used to inventive dining like many LTHers in the Chicago area are, you might be put off by what I would describe as fairly "safe" and even boring sides/presentations (e.g., mashed potatoes). That said, food quality is good and views are great.
2. Jackson Lake Lodge dining room - better than the above.
3. Jenny Lake Lodge -- Have not eaten here for dinner but had a lovely, reasonably-priced lunch here. I was surprised that for $10 or $11, you can get a delicious, fresh chicken salad sandwich or buffalo burger. Nice rustic setting.
4. Snake River Grill - We really liked this place. Had a great tuna tartare with fois gras, which was a featured appetizer when we were there. My husband also loved his pork shank in a mole, which I believe is their signature dish.
5. Snake River Brewery - agree with above posters. Good value.
6. Raven Grill - in Gardiner Montana. Best meal of the trip -- go there! If you're in the Mammoth Hot Springs area, Gardiner is 5 miles north . The Raven is kind of like "cowboy steakhouse" food -- but this is not a gimmicky joint like that may suggest-- This chef knows what he's doing. Had a succulent buffalo rib-eye and my husband had beef tips in a chimichurri presentation. Daughter had an awesome bufflao hot dog. Everything homemade, right down to the lemonade. Sides are phenomenal -- roasted corn, baked beans, great Texas toast. Attahced to Two-bit Saloon on Highway 89.
Enjoy!