How to monetize promo code website further?

I have a coupon/promo code website and it gets some decent traffic. Right now, I'm only monetizing it through adsense and the earnings quite frankly suck. I thought about adding a content locker and some really good coupons, but I haven't found any that work. I want to build an e-mail list from the site. but I wouldn't know what to market to people looking for promotional codes. Obviously they're trying to save some money and they're in a buyer mood, so maybe I can bank off that somehow? They're are some niche related cpa offers, but that didn't do so well either.

Any ideas?