Hi, Gary.
People are going to tell you that summer is the worst season for shooting in Yellowstone, but feel free to ignore them. Yes, fall and winter are better, but there's plenty for a photographer to do in any season.
Up around Mammoth is my favorite. You can do some great work with steam, snags and color of spring run-off at the upper terraces. I would especially encourage being there right after sunrise. Along the same lines (geothermics), the Norris Geyser Basin is underrated, the area around Grand Prismatic can look downright unreal, and the Upper Geyser Basin offers a lot if you have time and patience. Any of these are fantastic in warm back-light.
For more traditional landscapes, I like Blacktail Deer Plateau, the Lamar Valley and Dunraven Pass. You also can't go wrong with the Grand Canyon of Yellowstone -- the waterfalls are famous, but there are also plenty of spots for shooting the river, canyon outcrops, etc.
If you're shooting landscapes and your vehicle can handle this, there's a great dirt road that stretches from Mammoth to Gardiner, MT. Lots of rolling hills, grasslands, a small mountain lake, and you'll probably find some wildlife as well. It's a great location in morning light, and you'll probably be alone for the whole drive. Turn into and around the hotel, then right into the parking lot for the staff dorms. You'll find the road there, leading from the corner of the lot up and over a ridge.
As you noted, you're visiting during the busiest month of the year. Though I haven't experienced it myself, I've heard that traffic can get so bad in Yellowstone in July that if you pull your car over it can take as much as 15 minutes to pull back onto the road. Another traffic note: It can take a long time to get out of the Old Faithful parking lot immediately after an eruption.
The good news about traffic is that it sounds like you're shooting primarily in the magic-hour times of day, so you won't be much affected. Pretty much no one is on the road (except bison) before sunrise and after sunset. Driving can be slow during midday, but you should have plenty of time to scout and move between locations. And if you're willing to hike into the back-country, obviously you won't hit traffic there, either.
As for the Tetons, you can pretty much stop your car at any random moment and find great scenery. If you like to drive down side-roads, then the west side of the loop road will give you more opportunities for that. One in particular that I like is Signal Mountain Road; at the top you can shoot down at the valley and the Snake River -- a good spot for shooting compacted landscapes with a telephoto lens.
The Teton ranger staff is very helpful, too -- I definitely recommend talking to them. They can tell you good spots based on current weather conditions, and they know where the wildlife is. And if you're interested in the popular photo spots in the Tetons, there's actually a photographers' map for sale in the gift shops.
I hope some of this helps. Please feel free to contact me with any questions.
Best,
Chris
