I would love to connect my Spanish students in Maine with your classes. We started a Wiki in the fall in hopes of connecting with a school in Scotland. It did not work out, but you can get an idea of what my students had hoped to achieve if you visit. http://erskineamigos.wikispaces.com/
Hola, Mayte! Do you know the ePals projects? They are all free and are designed to encourage teachers from different places in the world to collaborate. Many teachers from South America have become part of ePals through Eduteka.
Projects include The Way We Are, Digital Storytelling, and multiple science projects (weather, water, habitat, climate change, natural disasters) and social studies (maps).