How to get more ads per page

Google limits standard publishers to 3 ads per page

Maximizing the value of them

 * Use the largest possible ads (not always true but generally)
 * Use the google heat map, to learn best positions for the ads
 * Accept graphical and video ads (annoying and not clear how much it helps)

Work-arounds

 * Google text links (that point to their ad pages) let you get a fourth ad
 * If you have an account manager, ask for an exception if your pages are very long
 * Break long pages into multiple pages

When that fails - what do many publishers do
I haven't done this but consider typical options including:
 * Chitika
 * Infolinks/Kontera
 * Video ads