The Harry Potter series is overall my favorite set of books of all time. I started reading em in 6th grade (I read dozens of books a month as a kid, no exaggeration...and not Goosebumps either
). It just captured my imagination like no other, and I was able to grow with the books as I grew...something that certainly benefits people who are currently I'd say 25 and under are more likely to be entrenched with Harry Potter for this reason.
However, there are certainly others I'd consider my favorite.
I'd say the list after HP goes like this
1) The Alchemist
2) The Great Gatsby
3) Catcher in the Rye
4) The Jungle
5) The Fountainhead
6) Fahrenheit 451
7) Moby Dick
8) 1984
9) Animal Farm
10) Angels and Demons
Honorable Mentions: The Crucible, The Da Vinci Code, Huckleberry Finn, Tale of Two Cities, Siddhartha, The Three Musketeers, Slaughterhouse Five