I usually tell my students that learning a language is like building a house: you need a strong structure, but you also need bricks. Otherwise, your house will look more like a skeleton! In a language, grammar is the structure and words are the bricks. Learning a lot of grammar but very little vocabulary won't help you at all to understand and be uderstood in that language.
Sometimes my students tell me that they find it difficult to memorize vocabulary and I usually reply that they should write lists of new words and try to translate them into their mother tongue; then do it the other way round: write the words in the native tongue and try to remember what the foreign word was.
Now, thanks to Mr. Byrne, of the Free Technology for Teachers blog, I've discovered Nabbber, a new tool that helps you learn vocabulary while being part of a social network. In Nabbber you can write the words you want to learn and then give the translation into your mother tongue or a definition in the same language, then you can also write an example so that you learn the new word in context. Furthermore, you can browse their web for other words that may interest you and you can also follow other people that have a similar level to yours. In order to help you remember the words you have contributed and the ones you have marked, there is the possibility of doing exercises and thus check your knowledge.
I find Nabbber quite an interesting tool for language learners. Give it a try!