Magento - Permissions

working with permissions - i have found many of our install problems have been permission based -  you should safely be able to set all directories to 755 and files to 644. with the exception of 

1. /media should be set to 775 
2. /var should be set to 775
3. /app/etc/ should be set to 775
4. /app/etc/local.xml should be set to 664
5. /var/.htaccess should be set to 664