There are a couple of ways to search for the registered agent of a company:

Westlaw is the quickest and easiest resource to use to find this type of information. The database to use would be Combined Corporate Records & Business Registration Records, the database identifier for which is CORP-ALL. You can also search states individually by using the state abbreviation such as CORP-CA for California. Other information that can be obtained from this database is the business address and date of incorporation or names and addresses of officers.

You can also find the registered agent of a company by going directly to the websites of the individual Secretaries of State. Rather than searching for each state website, a good resource that has created a page with links to all 50 states is the National Registered Agents, Inc. (NRAI). NRAI http://www.nrai.com is a professional registered agent service for business entities. One of the features on NRAI's website is their Research Center http://www.nrai.com. Within the Research Center, NRAI has provided links to State Online Databases, Secretaries of State, State Revenue Departments, State Insurance Departments, Banking Commissions and State Legislatures.

Once you select the Research Center page, there is a list of links on the left side. Select "State Web Links" and then on the next page select "Online Database" at the top of the page in the second column. This link will take you to a list of states with links to their corporate pages (called either Corporate Information, Corporate Inquiries, Corporate Database, Business Name Searches, Corporate Searches, etc.). Since each database is created by the individual state, the quality, availability and detail vary greatly. Some databases are free, some fee-based and some a combination of both. This resource can be good to use since some of the databases are free, sometimes the databases provide more detailed information than Westlaw, and sometimes they provide different information than Westlaw. It can either be a good place to start or a good place to double check your information. The down side is that it can be hit or miss depending on the state that you need to search.