Alright, despite being a sci-fi buff, I have not yet read any Heinlein. (Please include a thorough scoffing in your responses.)
I had hoped they were out of copyright, but, alas, they will still cost me to read on the Kindle. Thus, I must prioritize my reading as I'm not about to just randomly start downloading $8 books.
So, what is the APS recommendation for where to start?
SHUN THE HERETIC!!!
Trotting out stock answer - Webscriptions.net. Wait - are you wedded to the Kindle? Actually, even if you are, try Baen for slightly-cheaper Heinlein, though they don't have everything of his yet. They have books in multiple formats at Webscriptions.net, including, IIRC, Kindle format. No DRM.
You
***MUST*** read 'The Moon Is A Harsh Mistress'. All else is optional, though highly recommended.
Take that back. Read 'Starship Troopers' as well.
'Strangers In A Strange Land' and 'To Sail Beyond The Sunset' are... weird. 'Friday' is not bad, but not his best. 'Farnham's Freehold' is good. 'The Puppet Masters' is excellent. 'Tunnel In The Sky' (one of his youth/teen novels) was a favorite of mine for many years. 'The Door Into Summer' also. Actually, I suppose they still are. 'Job: A Comedy Of Justice' was entertaining - I'd rate it a little above 'Friday'.
For a bunch of his short stories and some nonfiction essays, read 'Expanded Universe'. His fantasy, as opposed to science-fiction,
I've read nearly everything of his - though not, astonishingly enough, 'Time Enough For Love', one of his classics (speaking of "SHUN THE HERETIC!!!"...), and find most of it worth keeping on my Droid, if I can find ebook copies. I have a bunch of them on the shelf in dead-tree form, as well.