What are the best 'Classic' novels for a 10 yo (as of March 24th) 5th grader?

I would like for him to "stretch his mind" in reading and I think many of the classics do that...just not sure which ones have language or situations that are not appropriate for his age.

Thanks!

TripleB

About 2 years ago, this crowd-sourced list was created for an 11 yo... some of the titles listed here may be of interest?