Do co-registration services pay people to subscribe, or offer other incentives?
There are lists (see the Freebie Seekers page of this Directory) that offer names of their members who opt in and are paid or offered to win something for doing so. Unless your offer has a similar theme (you want to give them something or pay them to be a lead) I would recommend caution on this kind of list. Personally, I don’t use them, because the participants might be more interested in the free gift than in the information they will later receive.