Take control of your flashcards + share them with friends
Quizlet.com is a great website for effectively learning vocabulary, for languages and anything else! For a quick video on how the whole thing works, check out the demo video. Cool fact: It was started by a 15-year-old high school student!
Basically, you can add and share vocabulary lists, make them public, private or share only with certain groups. Once you have them in the system (or you find an existing set you want to study), you can choose between several options for learning/familiarizing and self-assessment.
Use existing vocab sets to learn just about anything
There are already gobs of vocab sets available on the site - so many that individual attention is being brought to amazing collections available on the site, such as the HSK Test Vocabulary Preparation Pack and more.
Flexible, fun + free with super cheap upgrade available for power users
So take a look at Quizlet when you get the chance. It's likely that content already exists for what you need to study! I have added this to all the language sections even though there are not vocabulary stacks yet for all of these. Reason being you can use the site to create any vocabulary lists you want - it's wide open!