OpenX - Ad Server
OpenX is a quite popular and widely used Ad Server. It supports geo targeting, content targeting Ads, just create a zone and insert the html code in to the web page. The Ads will be served from your repository. It has multiple pricing models (CPM, CPC, CPA, Fixed Cost). It supports Image, Flash, HTML, 3rd party, Rich Media, Video (linear & non-linear) file formats.
OpenX could be extended using its API or plugin-framework. It provides detailed reporting of Ads published and clicked. Advertisers on the Market bid on your inventory in real-time, one impression at a time.