Determine what parenting philosophy you feel most comfortable with and choose a physician who is knowledgeable and supportive of those choices.
If you're breastfeeding, for example, make sure he has a nurse or lactation consultant on staff who can help you out. Beware the care practitioner who says they support breastfeeding but have tons of formula ads/posters in their office, or no educational material at all about nursing. Make sure they put their money where their mouth is, on all the issues you and your family feel are important.
If you plan to sleep with your baby, make sure s/he is not going to give you a ton of grief - rather, will educate you on safe cosleeping. Same goes with vaccinations, all the controversial subjects.
Consider going to a new mom or La Leche League group now, so you're not scrambling for resources with a new baby. There's usually lots of moms who can suggest pediatricians, and ones who will tell you who to stay away from based on their personal experiences. Just remember, a person others love is not necessarily the right fit for you and your baby. Don't be a member of the herd if you don't like where the pack is headed!
And consider pediatric nurse practitioners, too. They may be able to spend more time with you than the average ped.
Be prepared to change if you don't like the practitioner. It's ok to adjust to your families' needs as time goes on, or you find you're not compatible with your doc. Remember, trust yourself and your baby. You are your baby's best expert, and you will know your baby's unique signals and needs. Don't let people make you question your intuition too much. I had to fire my first family doc because she was simply uneducated about breastfeeding, and I needed a physician who was going to be supportive and knowledgeable.
Congrats, by the way! Becoming a parent is such a wonderful experience!
(And may I suggest you hire a doula for either birth or postpartum? We're great at helping new moms and dads, and helping to prevent postpartum depression!
Sorry guys, I gotta plug my profession. It's like a tic.