Earn more money with your blog using these free banner ad plugins by maximizing your ad space. They are compatible with WP 2.3.
Ad-minister
Ad-minister is a wordpress plugin that allows you to manage ads.
You can use it for for rotating banner ads and other static content.
Ads can be positioned by placing the plugin code directly in the
template or by using widgets. Many functions.
Multi-line AdRotator for WordPress
A very easy to use WordPress banner ad plugin. Widget compatible.
Or simply place one line of php code in your template
Got Banners WordPress Plugin
This is the one used by John Chow and Techcrunch (the 125 x 125 banners).
This banner rotating plugin displays all ads all the time. But they will appear in a random order on every page refresh.
Described previously: Rotating Banner Ads