All Experts
An all-volunteer service, with thousands of volunteers answering questions, from grammar to gardening. Free.

Amazon book search
Search by author, title and/or subject. Remember to change the setting for "sort results by" to, say, "publication date." Warning: The listings can be dirty, with typos and misspellings.

American Medical Association Doctor Finder
Virtually every licensed physician in the U.S. -- more than 650,000. Search by name or broad medical specialty. (You can find pediatricians, or ophthalmologists, but not pediatric ophthalmologists.) Another limitation: You have to know the state.

Ask an Expert
A directory of people who have agreed to answer questions, on just about any topic: magic, fishing, taxes, Judaism, etc.

Black Book
Some very interesting search choices offered at this investigation resource site. Of primary interest would be the "registering a sex offender center" link. Most of the other links are for books and services that can be purchased by investigation associations, but the site does have some other interesting resources, such as a P.I. (private investigator) licensing directory that can be searched.

Center for Ethics in Government:
If you're looking for registered lobbyists, contact the people listed here in order to get comprehensive, up-to-date information on who is doing what in any state. From the National Conference of State Legislatures.

Directory of Legal Academia
Lists U.S. law schools alphabetically. Also links to directories of lawyers and law organizations. From the Legal Information Institute, Cornell Law School.

Expert Net
An expert finder through universities in the U.K., similar to the Profnet service in the U.S. And now affiliated with Profnet.

ExpertCentral.com
Claims 4,500 experts in categories serious and frivolous. Though expertise is self-defined. Some questions are answered for free, "and sometimes the experts will propose a fee for helping you." So this is partly a way to find freelance workers of many types. Searchable, though the searching isn't well focused.

Experts.com
These folks paid at least $250 to be listed as experts.

FACSNET Reporter's Cardfile
Addresses, phone numbers and Web addresses for think tanks, advocacy groups, and special interests. (Registration required.)

Global Beat experts list
List of international experts, maintained by New York University. Categorized by region and issue.

GuestFinder.com
An online directory of more than 200 authors, experts, and spokespersons available for media interviews. "Guests pay a fee to be listed with GuestFinder. In exchange for an interview, guests wish to be mentioned as a source for any news article or story to which they contributed."

Martindale-Hubbell Lawyer Locator
More than 900,000 lawyers and law firms in the U.S. and elsewhere -- not all of them. But search the entire country at once.

National Conference of State Legislatures
Policy briefings on issues that come before state governments. Not only essential for statehouse reporters, NCSL is a good source of expertise for stories doing issues stories.

National Press Club news sources
A searchable directory of news sources and experts.

Noble Directory of Experts
These are people putting themselves forward as experts. Useful, but be careful.

ProfNet Experts Directory
A service connecting reporters to public relations people for universities, corporations, etc. A useful service. Send a question (to universities only, or to a broader group), and you get answers back that day. Be careful: Make your question specific.

Public Record Finder
Links to more than 6,000 free public record sites around the world. Search by keyword, or by category such as criminal and sex offenders, business or court records. Also find reference sites such as dictionaries and people finders or data sites on labor and transportation.

SourceNet
SourceNet, like ProfNet, allows posting of queries to agency and corporate public relations people. Unlike ProfNet, those postings are anonymous. You read the replies on the Web. Free registration is required. From MediaMap, a provider of information to public relations professionals.

Sources
More than 5,000 expert contacts and media spokespersons representing more than 1,000 organizations ready to answer media questions on their areas of expertise. A free service for journalists, writers and researchers. Based in Canada.

Sources and experts list from SLA
A good list kept by the Special Libraries Association. Compiled by Kitty Bennett of The St. Petersburg Times.

The Global Beat
A resource for journalists covering international issues, with background info, expert sources, and tips. From the Global Reporting Network, a program of the Center for War, Peace, and the News Media at New York University's Department of Journalism and Mass Communication.

West Legal Directory
More than 800,000 lawyers and law firms in the U.S. -- not all, but many. If you know the name, you can find the lawyer anywhere in the U.S. Or search by area of practice.

World Directory of Think Tanks
Japan's National Institute for Research Advancement has a massive list of major think tanks worldwide -- 320 from 77 regions. This site provides contact information along with short descriptions of what the think tank's focus is, lists of staff and publications, and brief background information.

Yearbook of Experts, Authorities & Spokespersons
OK, not all these folks are authoritative. But they probably know more about their subject than you do.