When you know the recipient’s name, sign it “Sincerely yours” or just “Sincerely”, or in the US “Yours truly” is acceptable. Don’t try anything more cutesy or friendly unless a) you know the recipient quite well and are certain you can be informal without seeming disrespectful, or b) you have a “trademark” letter ending that’s part of your public persona (and the talent and popularity to pull it off). Signature and printed name: Signing your name is a minimal assurance that you stand behind what was written.
To save your reader time and to call attention to your strengths as a candidate, state your objective directly at the beginning of the letter. Example: I am seeking a position as a manager in your Data Center. In such a management position, I can use my master’s degree in information systems and my experience as a programmer/analyst to address business challenges in data processing. If you have been referred to a company by one of its employees, a career counselor, a professor, or someone else, mention that before stating your job objective.