I'm a big LN reader of at least I think so but anyway, since what I would like to recommend got licences (No Game No Life), I'll give you this which all must be familiar with http://www.baka-tsuki.org/project/index.php?title=High_School_DxD
Even so, I personally think Its way better than it adaptation which is only natural http://www.baka-tsuki.org/project/index.php?title=My_Youth_Romantic_Comedy_Is_Wrong_As_I_Expected.
http://www.baka-tsuki.org/project/index.php?title=Rakudai_Kishi_no_Eiyuutan Do give this one a read. There are others but most of them has gotten an anime, will get one soon or has been licence but non the less, their better than their adaptions and they deserve to be read.
This series is great also but unfortunately, only one volume is translate so far http://hereticlnt.blogspot.sg/2014/05/clockwork-planet-v1-chapter-1.html