Query Shark:
http://queryshark.blogspot.com/
Miss Snark:
http://misssnark.blogspot.com/search/label/crapometer-cover letters
Evil Editor:
http://evileditor.blogspot.com/
Successful Queries and Submissions
http://www.writing-world.com/queries/index.shtml
Some Winning Query Letters
http://www.charlottedillon.com/QuerySamples.html
How to Write the Perfect Query Letter
http://www.guidetoliteraryagents.com/online-editor/how-to-write-the-perfect-query-letter