http://www.cervantes.es
Spanish Cultural Institute

http://www.euronews.com
Euronews: videos of daily news in a number of languages including Spanish

http://www.lenguayliteratura.com/
Very useful site for teachers and more advanced students.

http://www.comunicativo.net
Useful site for teachers. Contains lots of activities, exercises and lesson plans.

http://www.studyspanish.com
Tutorials and monitoring service for teachers.

http://www.teachspanish.com
Commercial site with some free items. Songs, lesson plans etc.

http://www.eleaston.com/spanish.html
A vast trove of exercises and other teaching resources from the United States.

http://ezinfo.ucs.indiana.edu/~jsoto/lengua.html
Some useful exercises on grammar

http://members.aol.com/maestro12/web/wadir.html
Web-based exercises

http://www.spainembedu.org
Site maintained by Consejería de Educación of Spain's embassy in Washington DC. Lots of useful material.

http://spanish.about.com/homework/spanish
Homework and lots of other material in and about Spanish