With this test, you can track your progress over time without having to wait for JLPT exams. It's very convenient and absolutely free. 

Info about the test: main page

Free registration: apply (select SPOT90 + Grammar90 + 漢字SPOT50 for the full test)

Interpreting the results (Japanese): results details

Natively allows you to browse hundreds of Japanese books by JLPT level. Remember that many of these books were written for native speakers so they can be quite challenging. Please don't give up!

This website collects articles from various Japanese news services. Every article has at least audio. You can also click on most of the words to check their definitions, kanji and sample sentences!

There are many concepts that are difficult to explain with words. These amazing illustrations can help you understand various grammar points, differences between similar words, onomatopoeia and many more!

A website for advanced learners and even natives ;) Polite Japanese can be really difficult but this website provides a nice introduction and discuss sample scenarios. You can even take a quick test to check your level.