Want to learn new words?

One-word-a-day free email-service (you need to create a free account)

http://www.owad.de 

Merrriam-Webster: Word of the Day (you can subscribe to their email service)

http://www.merriam-webster.com/word-of-the-day/

Website of the Spotlight magazine with a word-of-the-day function and a vocabulary archive

Synonyms at different levels. For each answer 10 grains of rice are donated through the World Food Program.

http://www.freerice.com/