Drop Down List

 <apex:selectList size="1">

         <apex:selectOptions value="{!UserList}"></apex:selectOptions>

      </apex:selectList>

-------------------------------------------------------------------

public List<SelectOption> getUserList() {

       List<SelectOption> options = new List<SelectOption>();

        options.add(new SelectOption('US','US'));

        options.add(new SelectOption('CANADA','Canada'));

        options.add(new SelectOption('MEXICO','Mexico'));

        return options;

   

    }