Recommended

So my library is pretty cool.

It has this cool feature where you can send a librarian a list of the books you love and they can recommend new books for you to try.... awesomeness.

This is what I got back:

I think you might like Feed, by M.T. 
Anderson.  It takes place in a future in which computers are implanted in 
humans, and there is a constant "feed" of advertisements and entertainment 
coming through.  Titus is the main character, and he's able to function well in 
that society, but when he befriends a young woman who can't, he has some tough 
choices to make.
 
Another possibility might be the series by George R. R. Martin, A Song of Ice 
and Fire, which starts with A Game of Thrones.  It takes place in a kingdom 
where the seasons are decades long due to climactic change, and several families 
are competing for the throne.  It's more epic than most of the other titles you 
said you liked, but since you had Philippa Gregory listed, this might be a good 
combination of the drama of the royal families and the compelling writing of the 
science fiction writers you mentioned.
 
Another post-apocalyptic novel is Little Brother, by Cory Doctorow, is about a 
17-year-old named Marcus who gets picked up by the Department of Homeland 
Security after a terrorist attack on San Francisco.  When he's finally released, 
the country has become a police state, and Marcus decides to fight back.
 
Genesis, by Bernard Beckett, sounds like another good one.  It takes place on an 
island at the bottom of the globe that was the only place that stayed stable 
after the ravages of the 21st century.  A young woman is trying to get into the 
Academy, but finds that not everything is what it seems.  One review describes 
the end as a "crushing final twist."
 
Also, have you read Uglies, by Scott Westerfield?  It's about a society in which 
everyone gets surgery at the age of 16 to become beautiful.  Tally, the main 
character, is required to spy on a group of teens that have escaped to avoid the 
surgery, otherwise she will remain "ugly" herself.  As she gets more involved 
with the group, she makes some grim discoveries.
 
A series that I found really compelling, but is historical fiction, rather than 
post-apocalyptic, is the Margaret of Ashbury series, by Judith Merkle Riley.  
The first one is A Vision of Light, in which a 14th-century woman is inspired to 
write her memoirs, only she can't write.  So with some effort, she finds a 
desperate monk who is willing to be her scribe, whom she tells the story of 
discovering her healing powers, which also get her accused of being a witch.  
It's quite a page-turner, and if you like it, there are more in the series.
 
Another historical fiction novel is Through a Glass Darkly, by Karleen Koen.  
It's the story of a young woman in 18th century England, who's parents marry her 
off to a man 26 years older than she is.  While she is thrilled, but her husband 
has ulterior motives for the match, and soon she comes to a crossroad that will 
alter her life.
 
Finally, have you read anything by Tracy Chevalier?  She's the author of The 
Girl with a Pearl Earring and The Lady and the Unicorn.  She's a tremendous 
historical fiction writer, and those two books imagine the stories behind 
Vermeer painting and the tapestry that hangs in the Cluny Museum in France.

Read any?