A formal cover letter should be accompanied by some form of a resume, CV, or portfolio (depending on your industry and job search) as these documents are usually held together in HR as supplementary to your application. Remember, hiring managers are looking to get as much data on you as possible and do not feel an obligation to seek information or materials from you. The application process is made easier for all parties if the applicant provides all materials up front, so make sure to include the documents you feel best represent you and what you can bring to any workplace with that awesome cover letter.