Spine Spline IK
Here is a simple way to construct a spine. This spine will give you quite a bit of control by keeping things really simple.

   

Bones
Build the spine

COG->spineA->spineB -> spineC -> spineD -> neckA -> neckB -> headA

   

Create Spline IK
Built an IK Spline with 1 as number of spans from spineA to neckA.

   

Create Clusters
Select the spline, go into component mode and select the top CV. Create a cluster (make sure that the relative option is turned on)

Name it:
shoulderCluster

Do the same with the middle and lower CV.
Name them:
middleCluster and lowerBackCluster.

   

Add Attributes to COG
Add Roll & Twist attributes to the COD joint.
Make them with -180 as minimum value and 180 as maximum value.

   

Connection Editor
Open the connection editor and constrain the Roll from the COG to the Roll from the spline IK. Select the COG and load it on the Left and load the spline IK on the Right. Now click on both Rolls to connect them.
Do the same with the Twist.

   

Parent Clusters to COG
Parent all the clusters to the COG joint.

That's it.

   

Download Maya file

Download tutorial