Mango Languages is an interesting site that has just begun. It provides free self-directed and bilingual online language courses, including ones for English for Spanish-speakers and English for Polish-speakers.
You have to register, but it literally takes seconds to do so. I don’t think it’s the best web application out there to help Spanish-speakers learn English, but it’s probably worth a visit.
I have the link on my Bilingual Exercises page under Spanish.