State that you have enclosed your resume and any supporting materials the employer may have requested (e.g., references, writing sample, portfolio, head-shot, etc.).
Re-emphasize how enthusiastic you are about the job and how your skills can benefit the organization. Thank your reader for his/ her consideration and mention how much you look forward to an interview.
Use an appropriate complimentary close such as "Sincerely" "Yours truly" or "Regards."
If you haven't had a response in 2-3 weeks, it's a good idea to follow up with a phone call (or email) to make sure your application was received and to reinforce your interest. You may also ask if it would be all right to call back within a certain time frame, just to check on the status of the hiring process. There is a fine line between being assertive and being annoying, so pay attention to what is said - tone of voice as well as words. If the job posting specifies "No calls" you should respect that.