The Oxford Spanish Dictionary by Study Spanish.com's verb lessons: a guide with conjugations, drills and quizzes organized by types of verbs.
Spanish Verb Conjugation Trainer: a JavaScript-Tool to practice the different forms of the most important basic and irregular Spanish verbs.
SpanishDict.com: website contains a 100 short, easy-to-understand explanations of Spanish Grammar topics. Each of the explanations is paired with 40 practice questions to test your knowledge
A Reference Grammar of Spanish by 
3000 Locuciones Verbales y Combinaciones Frecuentes by 
English Grammar for Students of Spanish, 7th Edition by For more books on Spanish Grammar, click on the subject heading link below.
