There is remarkably little information about safe maternal medication use or the effects on the fetus or neonate because obviously testing poses a problem. Newer medications often do not even have a pregnancy classification, so there is limited information. You can check with the various state teratogen registries. Some are online, like the Illinois Teratogen Information Service which has info on the most common and/or dangerous medications
http://www.fetal-exposure.org/ It mostly links to OTIS Organization of Teratology Information Specialists
http://www.otispregnancy.org/ so you may want to just start at OTIS. Other registries you have to call toll free.
A good book source is Medications and Mother's Milk by Thomas Hale. Though it appears directed toward medications during breastfeeding it does provides both lactation risk category and pregnancy risk category of common medications.
I would be interested in learning about other resources, too!