Register with Busuu.com to practice all aspects of the Spanish language. With Busuu you learn vocabulary and grammar based on exercises with pictures. You submit your written exercises to native Spanish speakers to correct, and you contact an online native speaker to practice your verbal skills. Busuu is free to register and to use the majority of the site, including some exercises. The components you pay for (pdf files and podcasts) are not necessary to learn the language.
Sign up for BBC's Weekly Spanish Tips (or their Spanish Steps if you are a beginner) and visit their Spanish language website daily. They offer a multitude of resources for the Spanish learner of every level, all for free. You do not need to pay to access any part of the site.
Supplement the above steps with the websites recommended by the Learn Spanish page complied by Lingolex and Best Spanish Websites from the University of Iowa.