Lucas has denied having any plans in mind for movies 7-9. I remember when I was a kid, the rumors were that there would be 9 movies, but Lucas' official statements in the last few years have been that it was always planned to be 6 movies, no more.
There are many books that continue the Luke/Han/Leia storylines. The "Heir to the Empire" trilogy is a good suggestion, but there's also the Jedi Academy trilogy, the Black Fleet Crisis trilogy, the young Jedi Knights books (Han + Leia's kids...), and solo stories like The Crystal Star and The New Rebellion.
Taking place about 25-29 years after "A New Hope" is a 21-book series called "The New Jedi Order" - it shows the invasion of the Star Wars galaxy by an alien race, this was followed by the Dark Nest trilogy, and then a 9 volume series called "Legacy of the Force". All of these feature Luke, Leia, Han and their extended families.
Right now, they're releasing a 9-volume series called "Fate of the Jedi", set about 43 years after "A New Hope".
The link below is to a list of books on Wikipedia, arranged mostly in chronological order. You can pick the era you most want to read about, and then search for those titles on Amazon.com -
