In terminal, first cd into the directory you want to chmod.

To CHMOD only directories to 755:

find . -type d -exec chmod 755 {} \;

To CHMOD only php files to 644:

find . -type f -name '*.php' -exec chmod 644 {} \;

This worked well to figure out permissions for my local WordPress install. I did have to specficially give my uploads directory write access, but it cleaned up all of the other files and folders.