Do you use them ? which are the best ad networks which offer popunder ads ( for publishers ). Also for what kind of sites these ads are more suitable ? Also if you don't like or use them. tell your why is that too.
If you have a loyal community on your site, or tons of unique visitors, you'll want to use popunders. If you are cash strapped and don't mind annoying your visitors a little, go with popunders from ValueClick and Casale, as their code is desiged to bypass most popup blockers, resulting in more revenue for you. On the other hand, people who have popup blockers are probably those that hate them, and they may never visit your site again.
There is a list of CPM programs at www.pay-per-impression.com and as was said here they are good if your site is not member based... But you could manage to make it as plus for your site... if you have paid membership you can switch off the ads for paying members. That way you could make even more
Pop unders are a great source of revenue and can actually be random content as opposed to targeted. I've had success running travel offers on marketing sites, so really any ad can convert.