Agreed, and adding Tunnel in the Sky specifically.revjay said:I can't just pick one but if it has Heinlein's name on it it is an excellent book. I'll just throw a few out there, Time enough for love, Stranger in a Strange Land, Rocket Ship Galileo, The Cat who walks through walls, Starship Troopers. Pick one its great.
Also E.E. Doc Smith's "Lensmen" series. Hugo Award winning SciFi, though it was based on some science since disproven. Supposedly there's going to be a movie based on them coming up.