I'm not going to try to reproduce the charts but I'll provide a link below. The Huddle Report has charts comparing the accuracy of the top 50 online mock drafts for the 2007, 2008, and 2009 drafts based on the following scoring system.
Each pick can score 1 or 3 points. Here is how: Player in round = 1 / Player in round 1 + matched to team 2 = 3 points.
There is another chart on the right side of the page that ranks the top 100 mock drafts for the 2009 draft only.
Here's the link.
http://www.thehuddlereport.com/Free/mockdraftscoring.shtml
Each pick can score 1 or 3 points. Here is how: Player in round = 1 / Player in round 1 + matched to team 2 = 3 points.
There is another chart on the right side of the page that ranks the top 100 mock drafts for the 2009 draft only.
Here's the link.
http://www.thehuddlereport.com/Free/mockdraftscoring.shtml