National Association of Professional Process Servers (NAPPS) maintains an updated, easily-searchable online listing of professionals around the U.S. The association only accepts members who have been registered as process servers for at least one year and can provide two letters of recommendation from legal services professionals, along with the annual fee.
Current members receive a list of new member applications and are able to object to any suspicious businesses. Once a server is admitted to NAPPS, they are held to a code of ethics outlining proper professional conduct with clients and subcontractors. Anybody called out for breaching contracts or otherwise conducting business unethically, will be blacklisted from the association. Finding a good server online through NAPPS.org is a pretty safe bet.