Wonderful Wikimedia Resources (Free Grammar Books and Phrasebooks)
Duolingo is a great resource for learning languages, but it needs to be supplemented. Here are some great resources from the same people who brought you Wikipedia:
http://en.wiktionary.org/wiki/Category:Phrasebooks_by_language - Phrasebooks for loads of languages
http://en.wikibooks.org/wiki/Subject:Languages - Wikibooks on Languages, where you can find tons of grammar books and other books about languages.
http://wikitravel.org/ - Thanks archaeopterix