Advertising module for OP

I don't think there are any good modules (none that we'd use anyway) specifically for OP or Drupal as a whole.

Try all of the great free advertising management systems on the market and see which suits you best.

We use DoubleClick for Publishers (Google Ad Manager) across our titles as it can do more that you'll ever need it to! You can filter ad delivery by user location, time zone, limit impressions delivered to each user/day/week/year and intelligently deliver campaigns with set impression target to deliver and rotate correctly.

It's not the easiest thing to get started with, but just stick with it, it's worth it.

If you only want to look at a Drupal module and no third party services, then try http://drupal.org/project/ad.

FYI, in the top right of drupal.org there's a search bar. If you search for what you're looking for and select 'modules' under 'refine your search', you should be able to find things easily.