My favorite was always 'Tunnel in the Sky', followed by 'The Day After Tomorrow' (aka, 'Sixth Column'), 'Door into Summer', 'Double Star', and 'The Puppet Masters'. Awesome stuff.
I re-read all the kids books too, officially to decide which ones to encourage my kids to read but mostly just to enjoy them. Starship troopers, Have space suit will travel, and Time for the Stars stick out, but they're all good.
After 'Stranger', it was like he quite being clever and went for the weird, becasue the combination of clever and weird is what made 'stranger' a hit. Maybe he just ran out of clever ideas and milked the weird. He churned that stuff out ad naseum. It was kind of sad really. My restrospective on Heinlen ended when I tried to read 'Friday'. I just couldn't get through it. His obsesion with sex seemed to overpower everything else.