Evidence based research:
Cochrane Database of Systematic Reviews
The Coalition for Improving Maternity Services
Evidence Based Birth
Improving Birth
VBAC Facts
Childbirth Connection

Birth Centers:
Special Beginnings Birth Center
Bay Area Midwifery
The Birth Center

Hospital Midwives:
Kathy Slone

Homebirth Midwives:
M.A.M.A.S Metro Area Midwives
Birthwise Midwifery

Support Midwives:
Maryland Families for Safe Birth
Maryland Friends of Midwives

Additional support:
Birth Options Alliance
Maryland Birth Network

Childbirth Classes:
Mindfulness-Based Childbirth Classes
The Bradley Method
Birthing From Within

Pregnancy Nutrition:
The Brewer Diet
Weston A. Price

Optimal fetal positioning:
Spinning babies

Steven Baron
Thrive Chiropractic
Laura Dover

CranioSacral Therapists:
Charlyn Santiago

Charlyn Santiago

Birth, Maternity, and Newborn Photography:
HeartLove Photography

Prenatal, Pospartum, and Infant Massage:
Jessie Bernstein

Placenta Encapsulation:
Placenta Benefits
Carmen Calvo
Wendy Matthews
Odile Penet 

Breastfeeding Support:
La Leche League International
Kelly Mom

Lactation Consultants:
Katy Linda

Cesarean Support:
International Cesarean Awareness Network (ICAN)

Postpartum Depression Support:
Postpartum Support International

Pelvic Floor Physical Therapist:
Andrea Lasner

This resource list is a compilation of both my personal experience as well as those highly recommended by others.
Check out my Lending Library to see what books are available for loan.
Feel free to add your suggestions to the list.