Seconding "A Fire Upon the Deep": a fast-paced, high-stakes action adventure in a zany, 5th Element-esque space opera universe. Explores the idea of strong AI in a unique and interesting way.

Love both of these. Perhaps more so "A Deepness in the Sky", with its darker tone, very thoughtful programming-related remarks, and the reversed "alien invasion" concept.

I really like how Vinge addressed the Fermi paradox by permitting that the constants of physics may not be different in different parts of the galaxy.

The first chapter (via Audiobook) was one of the best first chapters I've ever read / listened to. I was totally hooked after that.

Just about to chime in about Vernor Vinge myself - awesome conceptuals and well written

His books are great, I loved both "fire upon deep" and a "deepness in the sky". It is unfortunate he inspired the Singularity movement which I find full of bullshit and religious overtones.

Hitchhiker's matches nicely what you look for