I know this forum isn't the most active but for those who do follow it there is a Humble Books Bundles on Robotics at the moment.

https://www.humblebundle.com/books

For $15 you can get quite a selection of robotics books pdf format, for those who don't know how humble bundle works you can also pay less and not get the whole bundle.

I know most of the info in the books is out there on internet anyway if you look around but can be nice to have it put together. The full list of books isn't out yet they always release some later but will be more of same, normally another 3 or 4 books.

Just a heads up some here might find them useful and interesting.