I've just discovered three great resources for students and newer practicioners (like myself) of Spanish. All three are projects of Fundeú BBVA , a nonprofit organization formed to "collaborate in the good use of the Spanish language". All three are well worth a bookmark:

An excellent "dictionary" of dichos y refranes
 
Vademécum, where you can search for all sort of common mistakes and "made phrases" you may not recognize or be sure you're using correctly.
 
And the newest of the three, Wikilengua, a wiki of Spanish grammar, spelling, expressions and vocabulary. Here you'll find glossaries (of sports, "new" slang and extranjerismos, so far), a in-depth table of the words associated with places world-wide (ever wonder where abulenses live or what to call the residents of London in Spanish?), links to Spanish language dictionaries online, and lots more.
 
 
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