Not sure if I found all the options, but here is what I found:
XenCentral Ad Server by @XCentral
Ad Manager by @Robbo
[bd] Rotating Ads by @xfrocks
Digital Point Ad Positioning by @digitalpoint
Here are my questions:
1. Are there any others?
2. Which one would you recommend me to start with?
3. Which one do you use and why?
4. What are really the differences between the Ad Managment System listed above? I am kind of lost in them.
Thanks to all your replies.