I've been considering the following split:
Week A:\
Mon: Chest\
Tues: Arms\
Weds: Shoulders\
Thurs: Chest\
Fri: Arms\
Sat: Shoulders\
Sun: Rest
Week B:\
Mon: Legs\
Tues: Core\
Weds: Back\
Thurs: Legs\
Fri: Core\
Sat: Back\
Sun: Rest
i.e. 2 sets of 3 groups, alternate set each week
The idea...