This is is a question job-hunters often ask. And if they don’t ask it they should!
The email subject line should be interesting and compelling enough to make the recruiter want to read your email letter and your resume.
Use an email subject which describes you or the position you are seeking. For example, Senior R&D Professional or New Graduate Seeking Sales Position.
Non-specific subjects like Looking for a New Job or My Resume will not be enticing enough to encourage recruiters to open your email. In many cases, the title line (or a descriptive phrase) from your resume works well as the subject line for your emails.