Where can I find a good site to learn and practice Spanish online?

You can learn here

http://www.mansionspanish.com/

http://www.espagnolfacile.com/

http://www.splingual.com/

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A good place to start might be "About.com". They have a host of interactive language learning cites.

Good luck, mi hermano.

There are a lot of sites that where you can just fill in the blanks and check your answers. if you have a textbook, the publisher's site may also have useful links.