Before you start to use a trademark, you need to conduct a search. If you do not, your business may infringe on someone else's trademark, which can result in an unnecessary and expensive lawsuit. The most complete method of searching a trademark that I am aware of is the commercial database operated by Thomson-Reuters. In fact, the Thomson-Reuters database is the only database I know that attempts to maintain a comprehensive list of common law trademarks and trademarks registered in certain U.S. territories. However, the Thomson-Reuters database is also expensive - usually $500 or more for a complete domestic trademark search of Federal, State, and Common Law trademarks, as well as additional time from an attorney to review the results of the search, which can easily bring the total cost into the $1000-$2000 range. Many of the clients that I work with balk at the cost of conducting this kind of search.
If you want to conduct your own trademark search, entirely free of cost, I have assembled a number of resources, domestic and international, that you can use to see if the term that you want to use is clear of trademark issues. All of these are searchable in English.
Wrongful Termination Lawyer