[nrook]

Honestly in most genres you're hosed, but if you're into Japanese nerd stuff, j-novel club sells light novels (and a few manga) with no DRM.

[wintercarver]

Wait WHAT?! I’ve been buying ebooks off BookWalker and it’s so annoying. Their reader app sucks and they have these faux-protective constraints like not permitting a “copy” function on any highlighted text and limiting a book to no more than 50 highlights. It’s so silly… Edit: damn, had assumed you meant maximum nerd mode and that these books were available in Japanese… looks like it’s all English translations. So it goes.