I have been learning languages for 2 years now and wanted to share the resources/methods with all of you. 

1. Duolingo.com -- to learn from ground up, to practice writtten and listening. 

Pros : Free, Fast, Efficient

Cons: Doesn't help that much in speaking skills.

2. Talking to natives -- After you've got some hold of the target language it's time that you started talking to natives. In my experience practicing with a native is the best/fast way to improve in any language. This way we learn about their culture, country, places, lifestyle and we become good friends with passage of time. 

Sites like italki, papora, lingoglobe have a very rich community of sincere people looking for a language exchange.  

3. To improve further, we need vocabulary, expressions, idioms, proverbs. Few sites that have been a great help for me are :

1. Reverso Context : http://context.reverso.net/translation/

2. Wordreference : http://www.wordreference.com/

3. Vocabulary.com : http://www.vocabulary.com/

4. Tv series and movies with subtitles : Of course they help, all you need is more and more exposure. 

I have been through hundreds of sites, this is what I found best. If you know some other sites that have helped you a lot, please do share it in comments.