We are planning a driving vacation through Montana/Utah/Idaho/Wyoming in July. We will have our 4 and 7 year olds with us. What are the don't miss sights, attractions? Is it too late to make reservations for Yellowstone hotels? I would appreciate any and all recs. Our budget is pretty healthy so higher end accomodations would be o.k. if applicable.

That is a good piece of driving..but scenic all the way..
Yellowstone..will be crowded during July..and I would surmise that all of the Yellowstone Hotels are booked for the the summer..or at least over the 4th of July..also..the 24th is a State holiday in Utah and many of the folks from Utah head Yellowstone and the surrounding area...and there is usually not a hotel room to be had during this weekend either...Also..although there are a few old and nostalgic facilities in Yellowstone..I would say they are very basic..and rustic..but higher end they are not...I might suggest from the Montana side..staying in West Yellowstone, Montana..which is at the west entrance to the Park..they have several nice accomodations...Of course Jackson Hole...Grand Teton..are no brainers to see..and enjoy..Sun Valley Idaho is an option....I live in Utah and I am very familiar with all of the territory you are planning to explore..and especially regarding Utah and Wyoming and Idaho.. I can be helpful...but I do not know how much time you have..and I do not know which direction you are coming from or going to..and that would be somewhat strategic in the planning process or any sage wisdom I might think I have...You are welcome to contact me at my e-mail address with more specifics, or with questions you have and I will do my best to help.....

I just checked Yellowstone, limited basis, for a friend. The only thing left that I could find were rooms without a bath at Old Faithful Inn and the cheaper cabins at Old Faithful.
If I were in your position, I would try the motels in Red Lodge Montana, and West Yellowstone. West Yellowstone is not that far from the geyser basins and is full of motels. But, don't wait.
July is a bountiful month for the inn keepers!!

We will have 2-3 weeks available. We will be driving from Minnesota through South Dakota (black hills). We will want to spend some time in SLC with relatives at some point in the trip. Probably looking mid July 18-22 through early August 12-16th. Thanks for the help!

Summer ..if it is a multiple choice question I would opt for your August dates..no real reason other than you will miss the holiday crowds in YS..but it will still be crowded...If you are coming from the East..I would say to go thru Cody, Wyo..and make that your first stop....It will take you all day to see the Buffalo Bill Cody Museum..and it is worth it...then go thru the East entrance to YS..do your thing in YS ..do not cheat yourself on time in Jackson Hole or Grand Teton...you would have some time also to head out to West Yellowstone and perhaps spend some time in Island Park area of Idaho..or if you are into fly fishing the Virginia City-Ennis region in Montana on the Madison River..all short drives from YS..I think I would then recommend that you eventually end up coming out the south entrance of YS to Jackson..and head down 89.....and either cut over thru Bear Lake...Logan..Ogden..on your way to SLC..or go thru Evanston, Wyo pick up I-80 into SLC..In either case..if you have relatives in SLC I am certain that they can give you a few pointers..As mentioned if you want or need any specific info..feel free to contact me... will be happy to help..

We go to yellowstone once a year and by far, the best place to stay is in west yellowstone at hibernation station. That place was so fun. They're individual log cabins with a variety of configurations, but extremely nice. Auto gas fireplace. Daily maid service. You can get one with one queen bed up to like a three bedroom with full kitchen. The lodge inside the park is fun to visit, but sort of old. See the movie on the great fire at the west yellowstone museum or at the IMAX if it's playing there. You'll be amazed. The grizzly and wolf sanctuary was also very nice and interesting (the animals there have been rescued after injury or moved there rather than killed because of threats to ranchers). After 15 years, I finally got to see an actually wolf and grizzly bear close up (they're kept in large areas, not cages).

Don't Miss:

2-3 days in Yellowstone.
Stay at Old Faithfull Inn
Golden Spike Nat. Historic Site
Fossil Butte National Park (corner of WY)
Glacier Nat. Park

.. just a small list

Very, very often there are cancellations at the Yellowstone in-park hotels. Keep calling back weekly if not daily. You will get a room.

Fossil Butte is a small park in the corner of Wyoming in/near Kemmerrer (sp?). Wyoming has large number of dinosaur fossil finds. The visitor center and tour is very interesting, unique and educational. A nearby store sells 'tablets' with 50m year old fossils for $20

Golden Spike, (north of SLC and on the way to/from Idaho & Yellowstone) in the middle of nowhere, highlights the history behind the meeting of east and west railroad. Two competing RRs were building the last legs of an E-W line. A drive tour along the route gives a flavor of what it would have been like 150 years ago. Great museum.

Southern Utah has outstanding parks, if your driving route allows this. Don't miss Bryce CAnyon, Zion, Arches and many others. Plus, you will be very close to the North Rim of the Grand Canyon.

Limit your time around Salt Lake, as the city will is suffering from irrational Olympic fever & optimism, traffic is always bad and there are so many other places in Utah that are beautiful, and mid size cities are everywhere.