I've actually been making a list for my little brother... 11 or 12... somewhere in there. Recommended age in parentheses. I don't use them as a guide outside of roughly determining what order to read them in:
Huck Finn (12)
Tom Sawyer (12)
The Giver (11)
Flowers for Algernon (14)
Robin Hood (12)
Oliver Twist (12)
Hatchet (11)
Watership Down (11)
Animal Farm (13)
Ender's Game (12)
To Kill A Mockingbird (12)
Brave New World (14)
The Grapes Of Wrath (15)
Slaughterhouse-Five (15)
1984 (14)
The Absolutely True Diary of a Part Time Indian (14)
Where the Red Fern Grows (10)
The Diary of Anne Frank (12)
The Call of The Wild (12)
And The Devil Will Drag You Under (13)
Catcher in the Rye (13)
A few he's already read:
Bunnicula (9)
Hitchhiker's Guide (12)
Shiloh (9) (whole series)
White Fang (10)
Diary of a Wimpy Kid (9) (whole series)
And a fuckton of Goosebumps and Hardy Boys
Basically, if it's on a banned book list there's a good change it's up for consideration.
*edit: ZOMFG I forgot about Hank the Cowdog... I almost did a great disservice to syruptitious loaderation and the porcupine blues.