If you like the works of Robert A. Heinlein, and you know that Manson totally missed the point when he used "Stranger in a Strage Land" as his blueprint, then you might like
Spider Robinson. What do they have in common? Inventive science fiction, eccentric characters, and a similar writing style. If you prefer more of the "hard science" science fiction, then you might want to try
John Varley. If you want to see what Robert A. Heinlein would be like if he were born in a later generation (and possible took acid), then try
Cory Doctorow.