We are a group of HR monkeys and hiring managers who have worked with some of the largest search engines, vertical portals, and social-networking sites on the Internet, as well as for hardware and software manufacturers, universities, federal agencies, and accounting and consulting firms. In our jobs, we see thousands of cover letters and resumes every month. Some of them desperately need to be shared ;-)
My favorite so far:
"I don't know Craig personally but my friend told me about his list and I saw your job there."