Since this thread was resurrected, I'll just add that shortly after I started this thread in Sept 2000 I purchased AdvertPro, available at
It is not cheap, but an excellent program. Very flexible and I am able to deliver ads across the dozen websites (with different domains) I manage. I can set up multiple regions, multiple advertising accounts and run combinations of ads all over. Great for HTML/Rich Media ads as well.
It's not a recommended solution for single sites delivering only moderate amounts of ads, but definitely worth it if you have moderate to high requirements for an ad management solution.