Science fiction with mind-blowing philosophy and hard science, preferably without in-jokes.

I might buy a concrete and practical handbook and recommend it to my friends. For example, I did that with the anti-depression handbook "Feeling Good". However, they wouldn't read it.

Greg Egan, Charlie Stross, and Nick Bostrom's Dragonology were all effective doors to interesting discussions, discussions that indicated my friends "got it". Nick Bostrom's more academic-ish stuff just bounced.