Trusted online dictionaries - let's make a list :)

Hi,

let' share some links to useful English dictionaries online any type - collocations, synonyms, "general"...

I may start:

a) Oxford Learner's Dictionaries: http://www.oxfordlearnersdictionaries.com/
Many examples of use, sometimes etymology and idioms near main entry.
b) Online Collocation Dictionary: http://oxforddictionary.so8848.com/
It helps me a lot to make my writings more natural!

I'm looking for good synonyms dictionary (yeah, ideal synonymy doesn't exists, I know ;)) - anyone anything?

http://dictionary.reference.com/ - huge
http://www.ldoceonline.com/ - classic
http://www.macmillandictionary.com/ - ditto

http://www.urbandictionary.com/ - proceed with caution, here be pyrates!