I will occasionally look at the special offers on the HumbleBundle website, and at the moment there are a lot that look interesting to me! There is the Mad Scientist collection1, which includes books on making paper gliders, all the way through to rockets and drones. Then there is the DIY electronics collection2 of books on Arduino and Raspberry Pi for your various home projects. And if you want something about programming AI, there is the A.I. bundle3 covering a variety of topics from Statistics, and machine learning algorithms, to neural networks and Tensorflow.