Use the business letter format with the typical heading: your name, address, and the contact details for you and the recruiter. This is important in case your cover letter and targeted resume gets separated from each other in a huge stack on the recruiter's desk.
Also, address your letter to an individual. Include the hiring manager's name with "Mr." or "Ms." Nix the bland "Dear Hiring Manager" or "To Whom It May Concern." Nothing could be more generic. Be as specific as possible! Use the company's website or LinkedIn to find the name of the head of the department for the position you're applying for or the name of the hiring manager.