One of my favorite apps this year is one I paid for: Stick Pick. I love it. It's a digital version of the ole sticks in a can many of us have used to randomly pick students for a task.
I love Stick Pick because in AIS I have classes coming and going all day. One can of real sticks just wouldn't do it and multiple cans would be an organizational nightmare for me. Stick Picks allows me to have as many virtual cans as I need. I have one for each group. I haven't used the more advanced features that monitor students responses to questions, but it's something I hope to explore. I've used it to create random groups for peer projects, assign the order students will go in games, and for other times I've needed to pick students randomly. It works great in my fifth grade group. They are constantly asking to go next if I don't pull out the iPad and use Stick Pick. To me, this was $2.99 well spent.
You can find Stick Pick in the App Store.