Having students make flash cards in the classroom out of pen and paper is always a good learning experience — both in their creation and in their use.
Now there are countless sites on the web that allow students to make and use them online. As in quite a few of the activities on my site, I don’t necessarily see any major advantage to doing it online as opposed to doing it “old school.” It’s just a nice change of pace sometimes.
I’ve found five sites that are free and easy enough for English Language Learners of all levels to use. Students can create the permanent flash cards online and then they, or any other student, can access them.
Four sites that have been on my site for awhile are Flashcard Machine, Flashcard Exchange, Study Cards Online, and The Study Stack. I think they all function well, and it’s hard to say any one is better than the other. I just learned about the fifth one, Memorizable, and haven’t had the opportunity to check it out fully yet.