+1 for Stanslaw Lem, especially for the real geeks in the crowd. Unlike many/most sci fi authors, Lem was trained in mathematics and knew his hard sciences as well. The Cyberiad is funny and charming, but His Master's Voice is one of my favorites -- a glimpse at the dark side of the scientific-military-industrial complex and the unexpected possibilities inherent in scientific discovery, as well as the limits of human understanding.
Lem's story Golem XIV (in the quirky "collection" Imaginary Magnitude) consists of a long monologue from a superintelligent, former-military AI. I found it one of the stranger, more beautiful, and more compelling pieces of sci fi I've encountered.