If you are not happy with the CPM rates of ad networks, or CPC and CPA don't convert well with your site, you could try to find direct advertisers. However, have in mind that such an endeavor is not necessarily bound to succeed and if your site doesn't have audience advertisers can't reach elsewhere, you will hardly be able to negotiate good prices. Still, for some sites direct sales of ad space are a viable alternative and this is why you could also try it.
Openads Ad Server and OIO Publisher Ad Platform are two of the sites where you could try your luck. AdBrite also allowa you to price your ad space. In fact, almost any major network gives you the chance to put a widget on your site to invite advertisers directly to advertise on your site.
