phpAdsNew is an Open-source ad server that pc4media is trying out.
I used to maintain a number of ad serving software installations for a past client. Some were home grown and some were web based. I might just check this one out.
It requires PHP and MySQL. I just got an account over at Dreamhost to try, so I might set this up over there.
You'll know I tried it if you start seeing banner ads for my favorite videoblogs, reality TV shows, and friends start showing up in the sidebar.