You can also link to state medical board sites. Some of these sites have their own search engines for finding medical professionals. Health Pages is a growing site provided by New York Magazine. It allows you to search for doctors by state, county, name and practice specialty or for dentists by state, county and name. Not all states or counties are available yet, but site development is worth waiting for.
Bio information covers specialty, location, degree, hospital affiliation, etc.
Search contact info on 600,000 doctors by state of U.S. practice. Also great hospital profiles, including market data. Starting with a state entry, you can even search by partial name or perform a keyword search. Perhaps you are preparing a mailing to all the dentists in your area, so try a zip code search. Also, keyword search the site for dental school information, join in the newsgroup or check out the classifieds.