For anyone (like me) who accidentally jacks up all the file and folder permissions (i.e. 6XX, 7XX, etc.) here are the WP defaults you can reset to:
All FILES should have permissions set to 644
All DIRECTORIES (i.e. folders) should have permissions set to 755
It seems to be generally agreed that directories should not have 777 permissions, but sometimes that's the only (or easiest) way to get things working. So do that at your own risk.
Hope this helps others as it helped me.