Would it be illegal to sell eBooks on eBay?

I have a few eBooks that I have on my computer, I've actually acquired quite the collection. Is it illegal if I sell them on eBay? The books include authors such as Richard Dawkins, Stephen Hawking, Einstein, Carl Sagan, the complete works of Nietzsche and of Edgar Allan Poe, and many others. I ask this simply because I know it's legal to resell non-intellectual property, was just curious.