Actually, I have not read Farnham's Freehold, but Door into Summer remains one of my few auto-recs for Heinlein (the others are Starship Troopers, All You Zombies, Friday, and ). BUT, I reread it maybe 3-4 years ago, and was appalled at the decline in quality my copy had suffered while sitting quietly on my shelf. I'm afraid to reread it now.

Also, I refuse to recommend Stranger in a Strange Land to anyone in this lifetime. Ever.

Also also, the Niven sequel to Ringworld I apparently read before that one was called -- no, damme, it wasn't a sequel. I remembered it by its delightfully cheeztastic cover: it was The Integral Trees.