Also don't forget--if financial aid is even the slightest concern, going Early Decision will require you to commit to a school before seeing what they'll offer you. Also, most of the ED schools that I'm familiar with do not offer merit scholarships, either. I did Early Action back in the day (and was accepted!), but my alma mater has switched to ED.
If at all possible, see a dorm other than the one that's featured in a campus tour. I know at Brown the nicest freshman dorm, smack in the middle of campus, is the one they feature on tours. Unfortunately, a ton of first-years come in and expect their dorms to look like that one.
If school will be far from home, see how easy it is to get to the train station or airport without a car. A few weeks ago, I visited a friend from college who's getting his PhD at Stanford. It's not that easy to get to the campus to the train station, and even then you have a few transfers from the train station at Palo Alto to SFO. Also, shuttles and cabs can be less than reliable. In college, I almost missed flights waiting on a shuttle that was late, full, or never came.
Speaking of transportation--are there shuttles around campus to pick up students late at night from the library or other campus places? Especially if you're thinking of an urban campus, or one that's really spread out, this can be a huge safety issue.
Finally, let your child make the decisions! I know it's easier said than done, especially when you're the one paying. I really like how my parents stood back and gave me food for thought, but they didn't dominate campus tours or anything like that. Basically, they held their tongues until the admission letters came. I really appreciate that now, especially since I do college interviews for my undergrad and end up dealing with helicopter parents!
