"Advertising network refers to an
infomediary, which serves between a group (network) of web
sites (which want to host advertisements) and advertisers
which want to run advertisements on those sites.
Increasingly Ad networks are companies that pay software
developers as well as web sites money for allowing their ads
to be shown when people use their software or visit their
sites. Ad networks serve advertising on your website and
share advertiser revenue for qualified clicks each time your
site's visitors click on ads. An advertising network (also
called an online advertising network or ad network) is a
collection of (often unrelated) online advertising
inventory. When it is clear that the environment involved is
the Internet, companies who run or administrate such
networks are also called Advertising Agents or simply
Agents." – wikipedia.com
Here's
a list of some of the best ad-networks. Check them out to see
which ones are right for you.