I don't have a list on hand, but if you check the Mothering local forums those women are a wealth of information. I know the Chicago VBAC group also has a bunch since many women who want to avoid another c-section are getting doulas. Where are you located?
I'm using Birthways. They will ask you some preliminary questions and set you up with a doula based on your needs/wants/etc. I've met with ours a couple times and really like her.
Re: Doula recs
Tanya Mchale
www.tanyamchale.com