I think the first Heinlein book I read was "Have Spacesuit-- Will Travel".
I was pretty small, and I honestly don't recall much of the story, so I have no idea whether to recommend it or not. But it was always the signature Heinlein piece for me. When I think of Heinlein, that's the title I think of first.
[sip]
Ah... Sittin' in da airport bar... yet again.
There ya go. And Ramius...read it again. It's fun :)