Do you have a mobile app or a mobile-optimized interface? If so, you should mention it on the front page. I use Anki for studying vocabulary, and for reviewing I use the iPhone app exclusively. I only use the web interface for managing my lists. If you want to make a few bucks, you'll have no problem getting your users to cough up money for a mobile app, because of how handy it is to review in odd moments.
(I just checked Anki in the app store, and it's priced at $25 [1]. For the record, I paid less than that when I bought it, but I would have gladly paid $25.)
Also, make sure you test and advertise your support for non-ASCII characters and non-English dictionaries.