Useful links
Diccionario de
la Real Academia Española.
The DRAE is, in all probability,
the most authoritative dictionary in the Spanish language. It is also a
very useful tool, since it has a verb conjugation feature. When you type
a verb in the infinitive, simply click on the blue square to the left of
the definition and you will get the appropriate conjugation for that verb.
Diccionario panhispánico de dudas
The Diccionario panhispánico de dudas is a great tool. Its main purpose is to help clear any confusion and doubts about the differences in the use of the Spanish language among the various hispanic countries, as well as to clarify the finer grammatical points. Are you unsure whether you should say "le vi ayer" or "la vi ayer"? The DPD is the website to visit. Are you confused as to how to use commas in Spanish? The DPD has an answer for that too.
Grammar
exercises.
There are many websites with online language exercises, but I have found
this one very useful and simple to use. This site was created and is maintained
by Barbara Kuczun Nelson, from Colby College.
Newspapers and magazines.
If you are interested in reading in Spanish, here are some links to several reputable publications in Spanish: