Digital flashcards are a great way to help students study.  They help to track progress, can include audio, imagery and video and allow for multiple ways to study.  They are exceptionally convenient because they can be used with mobile devices (smartphones and other hand-held devices) so that students' entire flashcard library can fit in their pocket and is accessible at any time.  Two options for student-generated online flashcards are Flashcard DB and Quizlet. 

uses the Leitner System or Graded Spaced Repetition.  Quizlet has mobile apps for these devices