I try to keep it to a cover paragraph at best.
I only submit a cover letter when it is required and even then I prefer to keep it relatively short.
Here is some simple advice:
Once you finalize your resume, do a "Save-As PDF" with the PDF-settings set to [x] ISO 19005-1 compliant in MS-Office.
At every chance possible get this PDF into the hands of the recruiter and the people who will be interviewing you.
After you fill out the standard online application form and paste in your resume, try to attach the PDF. When the recruiter calls you and you start trading emails, send her the PDF. When you go to the interview, print 5 copies on resume paper and hand one over to each interviewer.
BTW, be sure to use Monster.com - that is how I got my present job.
Also check Craigslist ... seriously I know for a fact that Fortune 500 Companies sometimes post job ads on CL. Real jobs, not entry level.
If you are a PHD then you may have an uphill road, depending on your degree.
Good luck.