Avalanche Lake has a relatively easy, family friendly trail and is well worth the view of the Continental Divide behind the lake. There are some nice cascades (chutes?) along the way as well. We had the lake to ourselves for about 10 minutes, but it was midweek. The trail had hikers but it was not busy (July 2008). The trail feels smooth like a sidewalk when you are used to rocks and roots on some of the northeast trails.
It's a bit of a drive and more of a full day hike, but I'll second that the Grinnell Trail is pretty spectacular. Grinnell Lake has a beautiful turquoise color and there are falls coming off Salamander Glacier that are fantastic. We didn't get all the way out to the glacier as they were blasting snow off the last parts of the trail to open it up (I took some good video of the explosions).
We stayed for a week at cabins in the park and ate our meals there mostly, but one of the days we ate at a place called Two Sisters along a highway with not much else on it. Lots of license plates on the walls - it was a fun, loud place. After a long day hiking, it tasted good enough.
The surroundings in GNP are so stunning it's hard to describe. Have a great trip.