I’ve recently been playing with phpAdsNew, a PHP ad server system, for a work-related project, and I have to say, it’s a pretty solid piece of software. I’m very impressed.
It installs quick and painlessly, and you can add advertisers and build ad campaigns in no time. It comes with very nice PDF documentation—user, administrator, and developer guides. It has a good admin interface and rolls out a ton of stats and reports that blew me away. It’s definitely a “best of breed” PHP application (and those are rare).