For some time now, Google AdSense gives the option of blocking ads of certain sites through a competitor-filter. This can not only be used to fade out competitors but also for blocking ads of which you think that the clickprice could be slated rather low and whose blocking could raise your own revenues. Without comment, here a few inspirations:
Though this filter is also useful for ads which could be morally questionable:
The comments are open for relevant clues on other possible candidates. Apropos, the above hosts are all part of the one hundred most advertised, by my estimation.