Nouben ・ のうべん

Nouben　is a Japanese dictionary website with a twist...

Not only can you look up words and see example sentences, but you can look in detail at the Kanji for different levels of the JLPT exam and also take quizzes!

There is a great deal more to explore too and I think that it is a really useful learning tool.

Japanese Reading Tutor ・ リーディング チュウ太

Japanese Language Reading Tutorial System was developed to help native Japanese speakers as well as non-native Japanese speakers to learn to read Japanese at their own pace.

As well as an on-line dictionary in Japanese, English, Slovenian, Spanish, Dutch and German, there is a reading resource bank with explanations in Japanese, English and German.

The reading materials are graded by star -
1 star = easy 
2 stars = more difficult than 1 star
3 stars = more difficult than 2 stars

and they are mostly related to "all things Japanese" and so are very helpful for the comprehension part of the JLPT exam.

There are also some multiple choice quizzes in Japanese - I think that these are quite difficult!