Hmmm, I'm a very big reader in the scifi/fantasy section so...
Ender's Game by Orson Scott Card (I know it's already been said, but it's freaking epic)
The Belgariad/Mallorean Series by David Eddings
The Elenium/Tamuli series by David Eddings
Redemption of Althalus by David Eddings (Guess what, he's my favorite author

)
Hitchhikers Guide to the Ga;axy series by Douglas Adams
Pandora's Star/Judas Unchained by Peter.F.Hamilton (My favourite two books of all time)
The Wheel of Time series by Robert Jordan, later Brandon Sanderson (The very definition of epic. A not quite finished series of 14 books, and I was actually left feeling empty when I closed the third book after reading it. Awe-inspiring if you like high fantasy)
Harry Potter series (I know, I probably don't need to mention them, but they shouldn't be overlooked whatever you're into)
The Inheritance Cycle by Christopher Paolini (Eragon, etc.)
The Clayr trilogy by Garth Nix (Sabriel, Lirael, Abhorsen)
Against Gravity by Gary Gibson (Much heavier than the above books)
Mistborn trilogy by Brandon Sanderson (Win. Just win.)
The Black Book of Secrets by F.E.Higgins
the Armageddon Trade by Clem Chambers (My God, I never thought that a book based on financial terrorism could be so good)
Yeah, just get any of these out of a library. Out of these, the best is probably Pandoras Star and Judas Unchained.