The Strange Aliens of Abiogenisis
It has often been said that no human being can conceive of creatures that are truly alien to our world and to our experience. That is why so many aliens in science fiction basically just look like humans with prosthetics or, at best, humans in creature suits.
That may be true, but the works of Alex Ries come pretty close to what I would consider truly alien aliens. His illustrations give us a vision of what possible alien life may look like, while also keeping them well-rooted in plausible biology and credible anatomy.