The AdSense blog has outlined the maximum number of each type of ad unit their program policies allow.
It’s actually more than I thought, so helpful to get the official word on it.
In order for your pages with AdSense to be compliant, they must not exceed the following:
– video unit (currently only available in specific countries and languages, though we’re working to expand video units to additional publishers soon)
– AdSense for search boxes
– standard AdSense for content ad units, and
– 3 link units
Personally, I think this is excessive, unless you have a pretty long page with lots of text.