The links below connect you to sites with great interactive exercises in almost all the elements of Spanish grammar.  Students can use them to review and/or improve and teachers can use them to build reference materials for their students.

Sites for Spanish 1 and up:

Spanish for Beginners

EJERCICIOS DE ESPAÑOL

Más arriba: Spanish Language Exercises

Spanish grammar in review

Recursos gratuitos para profesores de español como lengua extranjera.

Sites for Spanish 3 and up:

Spanish Grammar Exercises

Colby College's Grammar Exercises

Spanish Subjunctive

Lessons for Intermediate and Advanced Students

Indiana's Ejercicicios de Gramatica

Spanish Language Self-Check Exercises

Ultralengua.net

Thematic links from the AP Central Web Site that will help you learn and/or teach about specific grammar points.