The Cosmopolitan has been running the $100 On Us promotion since it opened and they keep extending it. If you lose $100 in one day, they will give you $100 in Identity Play. You can only use the promotion once. The fine print specifies that this is for new members, but I am aware of existing members who have been able to take advantage of it as long as they had not used it when they signed up. The current promotion end date is November 30, 2013.

You can visit the Cosmopolitan promotions page for more details. That site will show the current promotion end date if they extend it again.
I highly suggest checking with the Identity players club desk before you play if you are an existing member and want to take advantage of the promotion.