SF Innovations have just launched Custard Pi 6
This card uses an I2C chip to drive 8 relays on a card.
As the I2C chip address can be set by the user, up to 8 cards can be daisy-chained allowing the user to control up to 64 relays from the Raspberry Pi.
Please see here for more information http://www.sf-innovations.co.uk/custard-pi-6.html
SF Innovations have provided resources for the software engineer in the form of functions that allow the relays to be switched On or OFF by using just 3 commands. Please see blog post on this here.
Full instructions provided on the website link above.