Bing, Google ads, TrafficVance, Lead Impact etc. I would also suggest you try retargeting ad companies. And on top of that email campaigns.
But as said this is only if you wish to go big since it can cost quite a lot.
Google ads might be a problem. I tried to advertise site in my sig, but they refused the ads and asked me to send them a gambling licence...which I don't have because I'm just a referral. If OP had this licence, Google might approve it, but not in all countries...
Yeah, we are aware of that, even with a license it's tricky.