My top ten (but not in any particular order) are:
1. J.K. Rowling- Harry Potter Series
2. Stephanie Meyer- Twilight and New Moon
3. J.R.R.Tolkien- Lord of the Rings
4. D. J. MacHale- Pendragon
5. Lois Lowry- The Giver, & so many more
6. Meg Cabot -Mediator Series
7. Shakespeare- enough said
8. Margaret Peterson Haddix- Shadow Children Series
9. Gail Carson Levine- Ella Enchanted, etc.
10. Ayn Rand- The Fountainhead
I know I'm missing so many authors, but I rtied to pick my favs from off the top of my head...