We went to Mammoth Falls and The Grand Canyon of Yellowstone. The canyon was one of my favorite places so far. We hiked down to the Lower Falls where we were standing right on the edge of the 300 ft drop. The water was high and the river was so wide and swift. We also visited the Upper Falls, then hiked along the South Rim 1 mile from the Upper Falls to Artist Point. Maggie was asleep in the car, so we got to hike carefree - John's parents watched her, then we took them down to see Artist Point, which is the best view we've seen. 
Fri Jun 12 2009 22:00 Yellowstone: Part 2:
We had a lot of fun our last few days in Yellowstone. We saw bears, elk, a fox, big horn sheep (including babies!), coyotes, pelicans, a parade of bison in the road, lots of geysers, hot springs and mud pots. We got to do an awesome 3.5 mile hike to Mystic Falls. We were lucky enough to see Old Faithful erupt from a viewpoint. Maggie loves hiking. John also took her to see some bison up close, but I was too scared. We saw Mud Volcano and Dragon's Mouth, which were really cool.