+1 for the Red Lion. That's basically it's sole reason for existing, and it does it well.
Advanced HMI is definitely an option, and it's free, but I personally don't like relying on a PC or a SCADA system to handle data transfer between PLC's. A PC running an application is just not on the same level as a purpose-built piece of hardware that has no other purpose in life, when it comes to reliability and ease of use.