By far, the most reliable of RTG based games sites, as regard no deposit bonuses. is Slots of Vegas. You can get a $25 real money bonus simply for registering. With no money needed, this is a true no risk situation.
While Slots LV also has RTG games as well as a lot more, they changed their popular $25 bonus into a wagering bonus. That means you have to deposit money first. That is not how we like our bonus offers.