Let's here about some of your favorite putting drills.
Two of my favorites are:
1. Take 4 balls and place them equi-distant from the hole in a perimeter fashion. This help get the feeling of the ball breaking in all possible directions.
2. Place 4 balls in a direct line away from the hole - about 7ft apart extending straight away from the hole. Start by putting the closest ball, then move outward and put the next ball, etc. It is really good for distance control practice.