http://www.instantbankroll.com/

This is the best that I am aware of.

I used this promotion for the $150 free bonus and everything went very smoothly. There are a few hoops to jump through and being a PSO promotion, I understand that you need to be sure that you jump through all of them perfectly. As long as you are prepared to take a couple of minutes to read instructions / terms and conditions (well worth it for the amount of money extra it makes you), you'll be fine.