Time Enough for Love is my favorite of his books.
If you add The Past Through Tomorrow and Stranger in a Strange Land you have the definitive Robert Heinlein.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)