I'm pleased to see how many people have read the Percy Jackson books. I was introduced to them a few years ago when my daughter read them for her 4th grade class. But even as an adult, I was instantly hooked and zipped right through the series. They are fast paced, light entertainment based on Greek mythology. Rick Riordan really knows his source material, and sticks to the spirit of the Greek myths while placing them in modern times.
I've also read every book in Marion Zimmer Bradley's Avalon series, though the original "Mists of Avalon" is by far the best. I've read it 3 times, and each time I get something different out of it.