There are all the obvious places in Yellowstone to see, but there are also some not so well known spots to stop in and visit. We were just there in August and spent a day on each of the two loops hitting the high spots and some of the lesser known areas.
The places we stopped at are in my blog
Arches, Geysers and Canyons. Check out the four days we were in Yellowstone. If you are going to drive the loops it is easy to stop in at the Sheepeater Cliff or the Petrified Tree. Calcite Spring gives you a nice view of the canyon. We are not hikers so most of the places we stopped required little or no hiking (walking).
Also in the Grand Tetons we took the boat shuttle across Jenny Lake for a much shorter hike into Hidden Falls. Without the boat it is a 5 mile round trip hike, with the boat a less than a mile hike.