Due to everything I have to teach, I find it hard to plan quizzes ahead of time. Things happen, so often your plans get rearranged. I have a couple doodling programs on the iPad and I can hold impromptu quizzes based on the right time in the class.
I throw a couple problems up on the board, have students do it on the iPad, hold up the answer and I've respond with a thumbs up or thumbs down. Sometimes, I have students raise a hand so I can go over and check their work. If its right I draw a smiley face, if not, I draw a frowny face.
There is no paper involved, makes it much friendlier than an official quiz and I don't have to count it if I don't want to. I can use it to ascertain where they are at this point in time. I can have them work additional problems if they are weak or cut it short and move on if they are doing well.
What I like best, is that the process takes 5 minutes and I have a decent assessment at the end of it. I have tests scheduled in two classes this week, so I'll run quizzes tomorrow to see if the students are ready for the tests or whether I should give them more practice.