I see that some shampoos are testing at a 6-7 and they dry my hair out, so I probably need to find something between 4-5.5.
Here is an article on the topic:
What is a Safe pH Level for Hair Care Products? eHow.com
Also The Natural Haven has a few educating post on ph levels too.
Also visit Luv Naturals for great video series about this topic!!
This post is very general in a sense and I'm still learning.