Interlex is such a discovery for me!
Things I like most are:
* I choose how I want to be asked my vocabulary - from native language to foreign or vice versa;
* it is me who's making the lists;
* I can kill my spare time trying to check my knowledge in German language I used to learn a hundred of years ago and still remember some stuff
A small range of vocabulary is already included into it
If I had known something that is worth paying attention I would already have shared it with you