Some resources that may help you:
Great sites to help proof your essays: http://linguee.com and http://spanishchecker.com
Grammar Practice by topic
Conjuguemos (more practice by topic)
About Spanish (more practice by topic)
Lyrics Training (fill in the blank songs in many languages)
Quizlet (vocabulary practice for all 18 chapters of Vistas search for Putzy)
Fun learning Spanish: Cool site with (interactive) crosswords and space invaders (scroll down to find other options)
Check your Spanish essay (Spanish checker)
Linguee check word choice / sentences / paragraphs