www.conjuguemos.com : Students can practice grammar and vocabulary from the class textbook in this site. Excellent for day-to-day practice and review.
www.wordreference.com : This site is an online dictionary, thesaurus, and verb conjugator. I find it useful for quickly looking up a word I didn't know. The dictionary provides discussion forums for people who have questions or comments. Excellent for providing diverse definitions from different Spanish-speaking countries.
http://www.spanish4all.com/ : An excellent resource, this site provides numerous links to dictionaries, grammar exercises, Spanish magazines, Spanish Online news, etc.
http://www.classzone.com/books/en_espanol_1/?state=MI : Students in Spanish I may practice and review vocabulary, grammar, whole chapters and sections straight from their book.
http://www.classzone.com/books/en_espanol_2/?state=MI : Students in Spanish II and III may practice and review vocabulary, grammar, whole chapters and sections straight from their book.