I'm pretty sure most picture books were meant to be read out loud, so I'm not going to touch on picture books. And again, most of the books I love to read aloud would probably capture the attention of 3rd-6th graders.
MY TOP PICKS
(This one is amazing, especially if you can do voices! There are some sensitive parts, that will require discussion)
(The Giver is the first book of an awesome trilogy. I have read Gathering Blue out loud, but it wasn't well received by my class. This is an example of a good book that isn't so great out loud! After that, I would read The Giver, and suggest the next two for independent reading.)
And, OF COURSE, the Harry Potter series by JK Rowling. (Now, I can do lots of voices, but the man who did the professional recordings of these books does about a hundred voices, literally. He is amazing!!!)
Other Good Ones!