Technically this doesn't fit with Classroom 2.0, but I think it rocks.
One of the games that comes standard on the iPod is Music Quiz. It will randomly play a part of a song you have loaded on your iPod and give you a list of 4 songs. You have to pick the correct song in the shortest amount of time.
Just the other day, Apple released iQuiz. Which does the same thing, but with updated graphics. And now today, iQuizMaker www.iquizmaker.com
was released. This allows you to make up your own quizzes and sync them to your iPod. You can also download and share quizzes on their site. Right now the software is only on the mac, but the PC version is coming in May.