755 (rw for user r for group, others). You must also make sure that the user's home folder has the others' x bit activated. You can do all of this inside a terminal window by typing the following commands (substitute [account-name] with the account's login name):
See http://en.wikipedia.org/wiki/Filesystem_permissions, section "Notation of traditional Unix permissions" for a detailed presentation and mapping between permissions and chmod numbers.
chmod g+x,o+x [account-name]
mkdir -p -m 755 /home/[account-name]/public_html
chown [account-name]:[account-name] /home/[account-name]/public_html