Most Banner Ads Don't Work
Why should i be interested in clicking your banner?
Is there something special about what you have?
Do you fill any of my specific needs (do you mention them)?
Why mention your company name, where is the mystery?
Banner blindness is a problem as well.
People click links much more often (as long as they don't look like adsense links)
If you have a network of sites, you are better of creating links rather than banners.