Sentence Mining
1. Tatoeba.org
Want to see how a specific word fits in a sentence? Tatoeba has 12,868,608 sentences in more than 428 languages including Brazilian Portuguese, some of them are examples with audio recorded from a native speaker.
2. Reverso Dictionary
A dictionary with lots of examples of a word in a sentence and also their individual meaning.
3. Linguee Dictionary
Another dictionary with definitions and lots of sentences as examples.
Monolingual Dictionaries
1. Caldas Aulete
Monolingual dictionary for the Brazilian Portuguese language, it contains a lot of examples and clear explanations in Portuguese.
2. Michaelis
Great definitions and examples, it also includes a popular idiomatic expression based on the word searched (not always happens though).
Books
1. Baixe Livros
Free downloadable e-books, works from famous Portuguese and Brazilian authors. Wide range of ages (good to test your current level of Portuguese).
Verbs
1. Conjugação.com
Want to know how a verb is conjugated?