Quizlet

One of my favorite education technology blogs "The Power of Educational Technology" by Liz Davis, recomended the website Quizlet.  This website is chalk full of premade flash cards covering a variety of subject areas, but I was most impressed by the ability for students and teachers to create their own flash cards and to develop study groups around shared flash cards.  There's even an iPhone application.

Check it out and feel free to post classroom uses and examples in the comments section.