I know there is an unending pool of online resources that encourage Spanish study, but I am always asked what my favorite sites are - so here they are (in somewhat random order):
1) Freerice.com
Simple word fun that sends money to the UN World Food Programme in the process!
Click on "Change Subjects" and you can do it in a number of languages & other disciplines!
2) Donquijote.org
Has many different activities and categories to choose from - easy-to-navigate website.
3) Quia.com/shared/spanish/
Quia is a textbook hosting website, but this particular link has all kinds of activities and drills for further practice.
AND MY ABSOLUTE FAVORITE IS:
4) http://www.lawrence.edu/fast/faresg/sites.htm
This guy has done it all and has wonderful links to thousands of resources. If you are a Spanish teacher and you do not have Dr. Fares in your bookmarks - do it NOW!
