It seems that a fairly frequent question that is asked in here is "Where do I find material at [level]". Even if you can read fluently now, I'm sure most people in here have had the question at some point - it is incredibly important for eventually become fluent (and not giving up on the way there!). Finding books which have enough complexity to learn from but are still easy enough to not make you want to pull your hair out can be challenging.
I've built a (beta) solution for this called Read Your Level: it helps you find books which match your current skill using an easiness score generated by an algorithm, as well as showing you the number of occurrences of each Kanji in the first 6000 characters. It links directly to the Amazon page, where you can download free kindle samples (you don't actually need a Kindle), see the description, reviews, etc.
The "easiness score" I've generated doesn't correspond to JLPT levels, but you should still find it useful, as it corresponds quite well to the difficulty of the text (as me and some Japanese friends have judged). I'm actively making improvements, so it should also improve over time.
For the moment, most books are from Amazon's kindle top 100s (both paid and free). Let me know if there are any books you'd like to see in the list - as long as I can get a free sample on Amazon with > 6000 characters, I can add it!
Also, it is free, but if you find it useful please let me know!
