I noticed there is a fair amount of suggested Community Promotion Ads that was rightfully discarded (i.e. mod-deleted) because it advertises the main site. I agree that this is redundant, since the ads would be shown on the main site itself, but some of the posts might have merit for other SE sites. So, maybe we could collect suggestions for other sites on the SE network as answers to this question. Maybe it sparks an idea where those outcast ads might fit.