Alert your visitors that they are using ad-blocking software and present them with a nice message telling them to switch it off for your site.
I created this plugin initially because I noticed that some ad-blocking software was blocking more than just my ads, they were also blocking random elements on my site like my image sliders as well. But obviously this will serve the guys who want it just for the purpose of notifying visitors who block ads to stop doing so.
This plugin displays a nice notice to them explaining the situation. The interface has two options, the okay button will reload the page upon clicking it (hopefully they would have disabled ad-block), the other button will simply close the message box. If the option to stop nagging visitors for the entire duration of their session on your website is set, then upon clicking the decline button, the message will only show again next time they visit your website.