I used Jodi Spencer for my birth last month. She's in South Jersey, but just over the bridge (I live in Philly- she got here super quick, too.) Jodi is fabulous and I can't say enough great things about her. Her website is http://www.beginswithbirth.com/
Choices in Childbirth publishes The Philadelphia Guide to A Healthy Birth. The guide includes listings for all types of birthing professionals. There is a great selection of local birth doulas in the '08/'09 edition.
You can download the PDF version of the file at the link above.