http://wordpress.org/extend/plugins/ad-minister/
The Ad-minister plugin provides basic ad management within WordPress. You can choose locations, insert code in your theme, then manage your banners from one location. It's like a simple version of openX.
http://www.openads.org/
OpenAds (previously phpAdsNew) is an open-source ad / banner server. It provides groupings, tracking, and various other features. It's mature software.
