Please visit http://www.immihelp.com/greencard-sponsors/
It shows the the database of all the employers who sponsored the greencard from financial year 2000 through 2008. You can look at the details of each petition, and you can also post experiences about a certain employer.
Everyone is encouraged to make use of it.
If anyone has any suggestions, feedback or bugs to report, please feel to post them here or contact us at any time.