Wordreference- An online dictionary that provides multiple contexts and can work Spanish-English and vice versa
Real Academia Española- The governing body of the Spanish language, site includes resources in grammar, historic and current digital dictionaries, an online library, and databases
Barron's 501 Spanish Verbs - A resource with verb conjugations in all tenses
100 Most Common Spanish Verbs - Common verbs you need to know and their conjugations