Dictionaries on the Internet

I want to share with you some resources to validate our orthography. Here they are:
- WordReference.com English-Spanish dictionary
http://www.wordreference.com
- Dictionary and Thesaurus - Merriam-Webster Online
www.merriam-webster.com
- Dictionary.com metabuscador de diccionarios
http://dictionary.reference.com
-Dictionary, Encyclopedia and Thesaurus - The Free Dictionary (metabuscador)
http://www.thefreedictionary.com/