The Moon is Harsh Mistress - excellent read.
Friday - a good read.
Number of the Beast - been a long time since I read it. It was interesting in high school.
Job: A Trajedy of Justice was a bit weird, but still entertaining.
Starship Troopers - A very good read.
Orphans of the Sky - a little bit different approach to your average SciFi book.
Tunnel in the Sky - A pretty good survival book.
Stranger in a Strange Land - An interesting story, a long read, and a lot of pseudoChristian crap. Not sure I would bother unless you really like Heinlein.
The Moon is a Harsh Mistress and Tunnel in the Sky are shorter books that are easy to start with. Friday a more recent book I think.
I like Heinlein and will have to look up some of the other books mentioned above.