(I apologize for the crappy formatting, this site sucks at making nice layouts with images.)
These are the highest quality books I can recommend:
The Wheel of Time: Authored by the incredible Robert Jordan, The Wheel of Time is my series (kinda like a sports team), the one that got me into fantasy like no other and filled my head with the desire to write. I will always be indebted to Mr. Jordan for writing these; they have changed my life in ways I can't even explain. Robert Jordan died several years ago, and Brandon Sanderson has taken up the challenge of finishing the series under the guidance of Mr. Jordan's widow, Harriet. These aren't just a series of books, they are a massive window into an even bigger, fully-formed world. So far there are thirteen novels released, and one prequel, with the concluding novel due sometime in late 2011 or early 2012.
The Way of Kings: Written by Brandon Sanderson, an author that has recently exploded into the public eye. This is an excellent book, and the first of a new ten-book epic series called The Stormlight Archive.
The Lord of the Rings: Composed by the immortal JRR Tolkien, I can't even conjure words to describe the profound effect these books have had on my mind and soul. If you were to read one Fantasy series in your lifetime, it should be this. Tolkien died a long time ago, but he left behind the greatest literary accomplishment ever (in my humble opinion). Please, please go read these books. You can read more about my thoughts on The Lord of the Rings in my post "Why Fantasy is Important".
Harry Potter: JK Rowling must be a witch herself (ugh, what a horrible joke) to conjure such amazing books. I grew up with Harry Potter, and these books have left a mark on me. The more I read them, the more I'm impressed by the polish and style of Rowling's work. The characters are great friends of mine, and I was sad to see them go. Like the other books on this list, these stand up to multiple readings. Full of whimsy, joy, sadness, and heart, Harry Potter is an important read.
The Kingkiller Chronicles: Pat Rothfuss did something to me that an author hasn't been able to do in a very long time: keep me up all night reading a book. Book One is "The Name of the Wind", and it's excellent. This series is so refreshing and somehow feels completely original (despite using basically the same building blocks as many fantasy books). I'll give you a hint: it's Pat's voice. Grrr, that ever elusive voice.