The summit trail is a great moderate-difficulty hike that can be completed by average hikers in about two hours, and much less if you're in particularly good shape (there were a number of people who appeared to run/jog the whole thing). Terrific views of the greater-Phoenix area, and lots of critters running around -- even at mid-day we saw squirrels, chipmunks, and several types of lizards.
Be sure to wear plenty of sun screen, and bring at least one full bottle of water per person. It can get quite hot, and there's very little shade on the trail (although there are a several good spots to stop and catch your breath, or just take in the views). Also note that the trail is quite popular. We were there on a Friday, and there was almost always someone in sight ahead or behind us. I imagine the weekends might be a bit over-crowded.