If your selling banner ads for your website, you may want to consider offering more options. On my sites, when someone buys advertising space, we give them a banner ad, a certain # of product placements, and blog posts about their business.
It gives the paid advertisers more bang for the buck. We kept our prices the same and it caused our ad sales to triple.

If you have any tricks for creative advertising share those here!

Leah Oviedo
Mercado del Mundo