Wormwood
Adventurer
Angcuru said:just don't do macbeth....dear lord don't do macbeth.

Our class did Macbeth as our 6th grade play (1981, Terra Centre Elementary, Burke VA).
Everyone had a blast---we took those great lines and ran with them! From the witches ("Eye of newt and toe of frog, wool of bat and tongue of dog.") to creepy Lady Macbeth ("Out damn spot") and the final swordfight ("Turn, Hellhound!")
The kids loved it and the parents loved it.
Even I had a great time, and I was just the dude who painted the sets and made the props for the witches.
You could do a LOT worse than Shakespeare. The only reason I didn't recommend it to Clay was because I assuemd he'd already considered it.
If not, check out: Shakespeare for Children (links)