I was going to post a response to Missy's comment about tips for obtaining a Culture Pass, but I figured it would be valuable information for everyone.
I don't recommend trying to get the passes from the Tempe library. They put the passes for the day out at random times to avoid mobbing. (Yes, I'm serious.) Therefore you have to just be very lucky to get passes for the hot ticket places(Zoo, Children's museum, science center, AZ museum for youth).
Each library branch has 5 tickets to each place, so I recommend trying a smaller branch of the Mesa or Phoenix libraries.
The tickets are "checked out" for a seven day period. It doesn't matter when you use the pass in the seven day period, it won't be available at the library again until it has come due on your card. Therefore each library might not even have all the different passes available every day of the week.
You might want to make friendly with the librarians to find out when different passes will be coming available. From my observations they don't appreciate people that are too pushy or try to get around the guidelines. On the day I got the passes to the Children's museum a woman and each of her kids checked out Phoenix zoo passes. So this one family had 3 of the 5 passes for the zoo. The librarian wasn't too keen on it, but they can't really refuse it.
Some of the museums have different times where admission is free. For example the zoo is free for kids all summer. Phoenix Children's museum is free the First Friday of the month from 6-10pm.
Check out the website for additional information http://www.showup.com/culturepass
If you have any tips or important info, please comment. I like to do things with military like precision and knowledge is power. (Yes, I'm that much of a control freak)